diff --git a/src/io/fopen_s.c b/src/io/fopen_s.c
index c01912aa..0bedaf41 100644
--- a/src/io/fopen_s.c
+++ b/src/io/fopen_s.c
@@ -79,6 +79,7 @@ EXPORT errno_t fopen_s(FILE *restrict *restrict streamptr,
                        const char *restrict filename,
                        const char *restrict mode) {
 
+    int l_errno;
     if (unlikely(streamptr == NULL)) {
         invoke_safe_str_constraint_handler("fopen_s: streamptr is null", NULL,
                                            ESNULLP);
@@ -97,6 +98,7 @@ EXPORT errno_t fopen_s(FILE *restrict *restrict streamptr,
         return ESNULLP;
     }
 
+    l_errno = errno;
     errno = 0;
     *streamptr = fopen(filename, mode);
 
@@ -106,6 +108,8 @@ EXPORT errno_t fopen_s(FILE *restrict *restrict streamptr,
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
         return errno;
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return EOK;
 }
diff --git a/src/io/fprintf_s.c b/src/io/fprintf_s.c
index 954718a8..95c45f66 100644
--- a/src/io/fprintf_s.c
+++ b/src/io/fprintf_s.c
@@ -72,6 +72,7 @@ EXPORT int fprintf_s(FILE *restrict stream, const char *restrict fmt, ...) {
     int ret;
     const char *p;
     out_fct_wrap_type wrap;
+    int l_errno;
 
     if (unlikely(stream == NULL)) {
         invoke_safe_str_constraint_handler("fprintf_s: stream is null", NULL,
@@ -92,6 +93,7 @@ EXPORT int fprintf_s(FILE *restrict stream, const char *restrict fmt, ...) {
         }
     }
 
+    l_errno = errno;
     errno = 0;
     wrap.arg = stream;
     va_start(ap, fmt);
@@ -103,6 +105,8 @@ EXPORT int fprintf_s(FILE *restrict stream, const char *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/freopen_s.c b/src/io/freopen_s.c
index 19b6b5ba..643c5d24 100644
--- a/src/io/freopen_s.c
+++ b/src/io/freopen_s.c
@@ -83,6 +83,7 @@ EXPORT errno_t freopen_s(FILE *restrict *restrict newstreamptr,
                          const char *restrict filename,
                          const char *restrict mode, FILE *restrict stream) {
 
+    int l_errno;
     if (unlikely(newstreamptr == NULL)) {
         invoke_safe_str_constraint_handler("freopen_s: newstreamptr is null",
                                            NULL, ESNULLP);
@@ -101,6 +102,7 @@ EXPORT errno_t freopen_s(FILE *restrict *restrict newstreamptr,
         return ESNULLP;
     }
 
+    l_errno = errno;
     errno = 0;
     *newstreamptr = freopen(filename, mode, stream);
 
@@ -110,6 +112,8 @@ EXPORT errno_t freopen_s(FILE *restrict *restrict newstreamptr,
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
         return errno;
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return EOK;
 }
diff --git a/src/io/fscanf_s.c b/src/io/fscanf_s.c
index 11fc294a..2e4c740c 100644
--- a/src/io/fscanf_s.c
+++ b/src/io/fscanf_s.c
@@ -86,6 +86,7 @@ any of the arguments corresponding to %s is a null pointer.
 EXPORT int fscanf_s(FILE *restrict stream, const char *restrict fmt, ...) {
     va_list ap;
     int ret;
+    int l_errno;
 #if defined(HAVE_STRSTR)
     char *p;
 #endif
@@ -126,6 +127,7 @@ EXPORT int fscanf_s(FILE *restrict stream, const char *restrict fmt, ...) {
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vfscanf(stream, fmt, ap);
@@ -136,6 +138,8 @@ EXPORT int fscanf_s(FILE *restrict stream, const char *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/gets_s.c b/src/io/gets_s.c
index 96ff8c06..0ccb0542 100644
--- a/src/io/gets_s.c
+++ b/src/io/gets_s.c
@@ -109,6 +109,7 @@ EXPORT char *_gets_s_chk(char *restrict dest, rsize_t dmax,
 #endif
 {
     char *ret;
+    int l_errno;
 
     if (unlikely(dest == NULL)) {
         invoke_safe_str_constraint_handler("gets_s: dest is null", NULL,
@@ -145,6 +146,7 @@ EXPORT char *_gets_s_chk(char *restrict dest, rsize_t dmax,
         }
     }
 
+    l_errno = errno;
     errno = 0;
     ret = fgets(dest, dmax + 1, stdin);
 
@@ -171,6 +173,8 @@ EXPORT char *_gets_s_chk(char *restrict dest, rsize_t dmax,
 #endif
         }
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/scanf_s.c b/src/io/scanf_s.c
index 95a4b8c4..50a5a672 100644
--- a/src/io/scanf_s.c
+++ b/src/io/scanf_s.c
@@ -87,6 +87,7 @@ any of the arguments corresponding to %s is a null pointer.
 EXPORT int scanf_s(const char *restrict fmt, ...) {
     va_list ap;
     int ret;
+    int l_errno;
 #if defined(HAVE_STRSTR)
     char *p;
 #endif
@@ -120,6 +121,7 @@ EXPORT int scanf_s(const char *restrict fmt, ...) {
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vscanf(fmt, ap);
@@ -130,6 +132,8 @@ EXPORT int scanf_s(const char *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/sscanf_s.c b/src/io/sscanf_s.c
index d25fb9ae..a180248a 100644
--- a/src/io/sscanf_s.c
+++ b/src/io/sscanf_s.c
@@ -89,6 +89,7 @@ EXPORT int sscanf_s(const char *restrict buffer, const char *restrict fmt,
                     ...) {
     va_list ap;
     int ret;
+    int l_errno;
 #if defined(HAVE_STRSTR)
     char *p;
 #endif
@@ -129,6 +130,7 @@ EXPORT int sscanf_s(const char *restrict buffer, const char *restrict fmt,
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vsscanf(buffer, fmt, ap);
@@ -139,6 +141,8 @@ EXPORT int sscanf_s(const char *restrict buffer, const char *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/tmpfile_s.c b/src/io/tmpfile_s.c
index ea54be35..8118aa17 100644
--- a/src/io/tmpfile_s.c
+++ b/src/io/tmpfile_s.c
@@ -80,6 +80,7 @@
 
 EXPORT errno_t tmpfile_s(FILE *restrict *restrict streamptr) {
     static int count = 0;
+    int l_errno;
 
     if (unlikely(streamptr == NULL)) {
         invoke_safe_str_constraint_handler("tmpfile_s: streamptr is null", NULL,
@@ -95,6 +96,7 @@ EXPORT errno_t tmpfile_s(FILE *restrict *restrict streamptr) {
         return ESLEMAX;
     }
 
+    l_errno = errno;
     errno = 0;
     *streamptr = tmpfile();
 
@@ -104,6 +106,8 @@ EXPORT errno_t tmpfile_s(FILE *restrict *restrict streamptr) {
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
         return errno;
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return EOK;
 }
diff --git a/src/io/vfprintf_s.c b/src/io/vfprintf_s.c
index 6e0cdb34..21ba4f00 100644
--- a/src/io/vfprintf_s.c
+++ b/src/io/vfprintf_s.c
@@ -71,6 +71,7 @@
 EXPORT int vfprintf_s(FILE *restrict stream, const char *restrict fmt,
                       va_list ap) {
     int ret;
+    int l_errno;
     const char *p;
     out_fct_wrap_type wrap;
 
@@ -100,6 +101,7 @@ EXPORT int vfprintf_s(FILE *restrict stream, const char *restrict fmt,
         }
     }
 
+    l_errno = errno;
     errno = 0;
 #if 0
     ret = vfprintf(stream, fmt, ap);
@@ -118,6 +120,8 @@ EXPORT int vfprintf_s(FILE *restrict stream, const char *restrict fmt,
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
 #endif
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/vfscanf_s.c b/src/io/vfscanf_s.c
index 49630b6f..f19dd22e 100644
--- a/src/io/vfscanf_s.c
+++ b/src/io/vfscanf_s.c
@@ -89,6 +89,7 @@ EXPORT int vfscanf_s(FILE *restrict stream, const char *restrict fmt,
     char *p;
 #endif
     int ret;
+    int l_errno;
 
     if (unlikely(stream == NULL)) {
         invoke_safe_str_constraint_handler("vfscanf_s: stream is null", NULL,
@@ -126,6 +127,7 @@ EXPORT int vfscanf_s(FILE *restrict stream, const char *restrict fmt,
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vfscanf(stream, fmt, ap);
 
@@ -134,6 +136,8 @@ EXPORT int vfscanf_s(FILE *restrict stream, const char *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/vprintf_s.c b/src/io/vprintf_s.c
index 7c660f6e..d75dccd3 100644
--- a/src/io/vprintf_s.c
+++ b/src/io/vprintf_s.c
@@ -67,6 +67,7 @@
 
 EXPORT int vprintf_s(const char *restrict fmt, va_list ap) {
     int ret;
+    int l_errno;
     const char *p;
 
     if (unlikely(fmt == NULL)) {
@@ -84,6 +85,7 @@ EXPORT int vprintf_s(const char *restrict fmt, va_list ap) {
         }
     }
 
+    l_errno = errno;
     errno = 0;
     ret = vprintf(fmt, ap);
 
@@ -92,6 +94,8 @@ EXPORT int vprintf_s(const char *restrict fmt, va_list ap) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/vscanf_s.c b/src/io/vscanf_s.c
index db999493..d57fdcd5 100644
--- a/src/io/vscanf_s.c
+++ b/src/io/vscanf_s.c
@@ -89,6 +89,7 @@ EXPORT int vscanf_s(const char *restrict fmt, va_list ap) {
     char *p;
 #endif
     int ret;
+    int l_errno;
 
     if (unlikely(fmt == NULL)) {
         invoke_safe_str_constraint_handler("vscanf_s: fmt is null", NULL,
@@ -119,6 +120,7 @@ EXPORT int vscanf_s(const char *restrict fmt, va_list ap) {
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vscanf(fmt, ap);
 
@@ -127,6 +129,8 @@ EXPORT int vscanf_s(const char *restrict fmt, va_list ap) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/io/vsscanf_s.c b/src/io/vsscanf_s.c
index b133af34..75f6be96 100644
--- a/src/io/vsscanf_s.c
+++ b/src/io/vsscanf_s.c
@@ -91,6 +91,7 @@ EXPORT int vsscanf_s(const char *restrict buffer, const char *restrict fmt,
     char *p;
 #endif
     int ret;
+    int l_errno;
 
     if (unlikely(buffer == NULL)) {
         invoke_safe_str_constraint_handler("vsscanf_s: buffer is null", NULL,
@@ -128,6 +129,7 @@ EXPORT int vsscanf_s(const char *restrict buffer, const char *restrict fmt,
     }
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vsscanf(buffer, fmt, ap);
 
@@ -136,6 +138,8 @@ EXPORT int vsscanf_s(const char *restrict buffer, const char *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/misc/bsearch_s.c b/src/misc/bsearch_s.c
index f65ce7f1..3d72d69f 100644
--- a/src/misc/bsearch_s.c
+++ b/src/misc/bsearch_s.c
@@ -118,6 +118,7 @@ _bsearch_s_chk(const void *key, const void *base, rsize_t nmemb, rsize_t size,
                void *context, const size_t basebos)
 #endif
 {
+    int l_errno;
     if (likely(nmemb != 0)) {
         if (unlikely(key == NULL || base == NULL || compar == NULL)) {
             invoke_safe_mem_constraint_handler(
@@ -153,6 +154,7 @@ _bsearch_s_chk(const void *key, const void *base, rsize_t nmemb, rsize_t size,
 #endif
     }
 
+    l_errno = errno;
     errno = 0;
 
     while (nmemb > 0) {
@@ -169,6 +171,8 @@ _bsearch_s_chk(const void *key, const void *base, rsize_t nmemb, rsize_t size,
             nmemb -= nmemb / 2;
         }
     }
+    if (0 == errno)
+        errno = l_errno;
     return NULL;
 }
 
diff --git a/src/os/getenv_s.c b/src/os/getenv_s.c
index 7c0bebee..17d0289d 100644
--- a/src/os/getenv_s.c
+++ b/src/os/getenv_s.c
@@ -102,6 +102,7 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
 {
     const char *buf;
     size_t len1;
+    int l_errno;
 
     if (likely(dest)) {
         if (destbos == BOS_UNKNOWN) {
@@ -142,6 +143,7 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
         return ESNULLP;
     }
 
+    l_errno = errno;
     errno = 0;
 #ifdef HAVE_SECURE_GETENV
     buf = secure_getenv(name);
@@ -178,6 +180,8 @@ EXPORT errno_t _getenv_s_chk(size_t *restrict len, char *restrict dest,
         if (dest)
             strcpy_s(dest, dmax, buf);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return EOK;
 }
diff --git a/src/str/strtok_s.c b/src/str/strtok_s.c
index 5a019f6f..1ac892a8 100644
--- a/src/str/strtok_s.c
+++ b/src/str/strtok_s.c
@@ -185,6 +185,7 @@ EXPORT char *_strtok_s_chk(char *restrict dest, rsize_t *restrict dmaxp,
     rsize_t dlen;
     rsize_t slen;
     rsize_t dmax;
+    int l_errno;
     const char *orig_dest = dest;
 
     if (unlikely(dmaxp == NULL)) {
@@ -256,6 +257,7 @@ EXPORT char *_strtok_s_chk(char *restrict dest, rsize_t *restrict dmaxp,
      */
     dlen = *dmaxp;
     ptoken = NULL;
+    l_errno = errno;
     errno = 0;
     while (*dest != '\0' && !ptoken) {
 
@@ -304,6 +306,8 @@ EXPORT char *_strtok_s_chk(char *restrict dest, rsize_t *restrict dmaxp,
      */
     if (ptoken == NULL) {
         *dmaxp = dlen;
+        if (0 == errno)
+            errno = l_errno;
         return (ptoken);
     }
 
@@ -357,6 +361,8 @@ EXPORT char *_strtok_s_chk(char *restrict dest, rsize_t *restrict dmaxp,
         dlen--;
     }
 
+    if (0 == errno)
+        errno = l_errno;
     *dmaxp = dlen;
     return (ptoken);
 }
diff --git a/src/str/vsnprintf_s.c b/src/str/vsnprintf_s.c
index fa53ab42..e0388d84 100644
--- a/src/str/vsnprintf_s.c
+++ b/src/str/vsnprintf_s.c
@@ -1480,6 +1480,7 @@ EXPORT int _vsnprintf_s_chk(char *restrict dest, rsize_t dmax,
 {
     const char *p;
     int ret;
+    int l_errno;
 
     if (unlikely(dest == NULL || fmt == NULL)) {
         invoke_safe_str_constraint_handler("vsnprintf_s: dest/fmt is null",
@@ -1514,6 +1515,7 @@ EXPORT int _vsnprintf_s_chk(char *restrict dest, rsize_t dmax,
         }
     }
 
+    l_errno = errno;
     errno = 0;
     ret =
         safec_vsnprintf_s(safec_out_buffer, "vsnprintf_s", dest, dmax, fmt, ap);
@@ -1544,5 +1546,7 @@ EXPORT int _vsnprintf_s_chk(char *restrict dest, rsize_t dmax,
         *dest = '\0';
 #endif
     }
+    if (0 == errno)
+        errno = l_errno;
     return ret;
 }
diff --git a/src/str/vsprintf_s.c b/src/str/vsprintf_s.c
index 69095c4b..0c7e9c30 100644
--- a/src/str/vsprintf_s.c
+++ b/src/str/vsprintf_s.c
@@ -103,6 +103,8 @@ EXPORT int _vsprintf_s_chk(char *restrict dest, const rsize_t dmax,
 #endif
 {
     int ret;
+    int l_errno = errno;
+    errno = 0;
     ret = _vsnprintf_s_chk(dest, dmax, destbos, fmt, ap);
 
     if (unlikely(dmax && ret >= (int)dmax)
@@ -111,12 +113,11 @@ EXPORT int _vsprintf_s_chk(char *restrict dest, const rsize_t dmax,
 #endif
     ) {
         handle_error(dest, dmax, "vsprintf_s: len exceeds dmax", ESNOSPC);
-#ifdef HAVE_MINGW32
-        errno = 0;
-#endif
         return -ESNOSPC; /* different to the standard (=0),
                             but like all other implementations */
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/fwprintf_s.c b/src/wchar/fwprintf_s.c
index 12055102..3ffc9e1a 100644
--- a/src/wchar/fwprintf_s.c
+++ b/src/wchar/fwprintf_s.c
@@ -80,6 +80,7 @@ EXPORT int fwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
     wchar_t *p;
     va_list ap;
     int ret;
+    int l_errno;
 
     if (unlikely(fmt == NULL)) {
         invoke_safe_str_constraint_handler("fwprintf_s: fmt is null", NULL,
@@ -109,6 +110,7 @@ EXPORT int fwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vfwprintf(stream, fmt, ap);
@@ -119,6 +121,8 @@ EXPORT int fwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/fwscanf_s.c b/src/wchar/fwscanf_s.c
index 45478fbd..60ec34ab 100644
--- a/src/wchar/fwscanf_s.c
+++ b/src/wchar/fwscanf_s.c
@@ -88,6 +88,7 @@ EXPORT int fwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
     va_list ap;
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(stream == NULL)) {
         invoke_safe_str_constraint_handler("fwscanf_s: stream is null", NULL,
@@ -104,7 +105,6 @@ EXPORT int fwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
     }
 #ifdef HAVE_MINGW32
     if (unlikely(!*fmt)) {
-        errno = 0;
         return EOF;
     }
 #endif
@@ -133,6 +133,7 @@ EXPORT int fwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vfwscanf(stream, fmt, ap);
@@ -143,6 +144,8 @@ EXPORT int fwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/mbsrtowcs_s.c b/src/wchar/mbsrtowcs_s.c
index 7ec6e616..6fc53fb5 100644
--- a/src/wchar/mbsrtowcs_s.c
+++ b/src/wchar/mbsrtowcs_s.c
@@ -134,6 +134,7 @@ EXPORT errno_t _mbsrtowcs_s_chk(size_t *restrict retvalp,
     wchar_t *orig_dest;
     mbstate_t orig_ps;
     errno_t rc;
+    int l_errno;
 
     CHK_SRC_NULL("mbsrtowcs_s", retvalp)
     *retvalp = 0;
@@ -184,6 +185,8 @@ EXPORT errno_t _mbsrtowcs_s_chk(size_t *restrict retvalp,
     orig_dest = dest;
     memcpy(&orig_ps, ps, sizeof(orig_ps));
 
+    l_errno = errno;
+    errno = 0;
     *retvalp = mbsrtowcs(dest, srcp, len, ps);
 
     if (likely(*retvalp < dmax)) {
@@ -198,7 +201,7 @@ EXPORT errno_t _mbsrtowcs_s_chk(size_t *restrict retvalp,
     } else {
         if (dest) {
             size_t tmp = 0;
-            errno = 0;
+            // errno = 0;
             /* with NULL either 0 or -1 is returned */
             if (*retvalp > RSIZE_MAX_WSTR) { /* else ESNOSPC */
                 tmp = mbsrtowcs(NULL, srcp, len - 1, &orig_ps);
@@ -214,6 +217,8 @@ EXPORT errno_t _mbsrtowcs_s_chk(size_t *restrict retvalp,
             rc = ((size_t)*retvalp == 0) ? EOK : errno;
         }
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return RCNEGATE(rc);
 }
diff --git a/src/wchar/mbstowcs_s.c b/src/wchar/mbstowcs_s.c
index 7cc56b03..a1950f09 100644
--- a/src/wchar/mbstowcs_s.c
+++ b/src/wchar/mbstowcs_s.c
@@ -130,6 +130,7 @@ EXPORT errno_t _mbstowcs_s_chk(size_t *restrict retvalp, wchar_t *restrict dest,
 {
     wchar_t *orig_dest;
     errno_t rc;
+    int l_errno;
 #ifdef HAVE_CYGWIN64
     mbstate_t st;
 #endif
@@ -180,6 +181,7 @@ EXPORT errno_t _mbstowcs_s_chk(size_t *restrict retvalp, wchar_t *restrict dest,
 
     /* hold base of dest in case src was not copied */
     orig_dest = dest;
+    l_errno = errno;
     errno = 0;
 
     *retvalp = mbstowcs(dest, src, len);
@@ -196,7 +198,7 @@ EXPORT errno_t _mbstowcs_s_chk(size_t *restrict retvalp, wchar_t *restrict dest,
     } else {
         if (dest) {
             size_t tmp = 0;
-            errno = 0;
+            // errno = 0;
             if (*retvalp > RSIZE_MAX_WSTR) { /* else ESNOSPC */
                 tmp = mbstowcs(NULL, src, len);
             }
@@ -212,6 +214,8 @@ EXPORT errno_t _mbstowcs_s_chk(size_t *restrict retvalp, wchar_t *restrict dest,
             rc = ((size_t)*retvalp == 0) ? EOK : errno;
         }
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return RCNEGATE(rc);
 }
diff --git a/src/wchar/snwprintf_s.c b/src/wchar/snwprintf_s.c
index c5c21e39..a3350bfb 100644
--- a/src/wchar/snwprintf_s.c
+++ b/src/wchar/snwprintf_s.c
@@ -126,6 +126,7 @@ EXPORT int snwprintf_s(wchar_t *restrict dest, rsize_t dmax,
     va_list ap, ap2;
     wchar_t *p;
     int ret = -1;
+    int l_errno;
     const size_t destsz = dmax * sizeof(wchar_t);
 #if !(defined(SAFECLIB_HAVE_C99) && !defined(TEST_MSVCRT))
     const size_t destbos = BOS_UNKNOWN;
@@ -188,6 +189,7 @@ EXPORT int snwprintf_s(wchar_t *restrict dest, rsize_t dmax,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     /* C11 solves the ESNOSPC problem */
 #ifdef HAVE_VSNWPRINTF_S
@@ -242,6 +244,8 @@ EXPORT int snwprintf_s(wchar_t *restrict dest, rsize_t dmax,
         return ret;
     }
 #endif
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/swprintf_s.c b/src/wchar/swprintf_s.c
index fde54177..36b57601 100644
--- a/src/wchar/swprintf_s.c
+++ b/src/wchar/swprintf_s.c
@@ -123,6 +123,7 @@ EXPORT int swprintf_s(wchar_t *restrict dest, rsize_t dmax,
     va_list ap, ap2;
     wchar_t *p;
     int ret = -1;
+    int l_errno;
     const size_t destsz = dmax * sizeof(wchar_t);
 #if !(defined(SAFECLIB_HAVE_C99) && !defined(TEST_MSVCRT))
     const size_t destbos = BOS_UNKNOWN;
@@ -189,6 +190,7 @@ EXPORT int swprintf_s(wchar_t *restrict dest, rsize_t dmax,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     va_copy(ap2, ap);
@@ -199,14 +201,15 @@ EXPORT int swprintf_s(wchar_t *restrict dest, rsize_t dmax,
     if (unlikely(ret == -1)) {
         if (unlikely(dmax == 1))
             goto nospc;
-        errno = 0;
         if (likely(dmax < 512)) { /* stacksize 2k */
             static wchar_t tmp[512];
+            errno = 0;
             va_start(ap2, fmt);
             ret = vswprintf(tmp, 512, fmt, ap2);
             va_end(ap2);
         } else {
             wchar_t *tmp = (wchar_t *)malloc(dmax * sizeof(wchar_t));
+            errno = 0;
             va_start(ap2, fmt);
             ret = vswprintf(tmp, dmax, fmt, ap2);
             va_end(ap2);
@@ -214,7 +217,8 @@ EXPORT int swprintf_s(wchar_t *restrict dest, rsize_t dmax,
         }
         if (ret > 0) {
         nospc:
-            errno = 0; /* EOVERFLOW */
+            if (0 == errno)
+                errno = l_errno;
             handle_werror(dest, dmax, "swprintf_s: len exceeds dmax", ESNOSPC);
             return -(ESNOSPC);
         }
@@ -227,6 +231,8 @@ EXPORT int swprintf_s(wchar_t *restrict dest, rsize_t dmax,
         strcat(errstr, strerror(errno));
         handle_werror(dest, dmax, errstr, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/swscanf_s.c b/src/wchar/swscanf_s.c
index d8eb252d..cdf3af9b 100644
--- a/src/wchar/swscanf_s.c
+++ b/src/wchar/swscanf_s.c
@@ -90,6 +90,7 @@ EXPORT int swscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
     va_list ap;
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(src == NULL)) {
         invoke_safe_str_constraint_handler("swscanf_s: src is null", NULL,
@@ -134,6 +135,7 @@ EXPORT int swscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vswscanf(src, fmt, ap);
@@ -144,6 +146,8 @@ EXPORT int swscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, (void *)src, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vfwprintf_s.c b/src/wchar/vfwprintf_s.c
index ba0447d2..36d36bd2 100644
--- a/src/wchar/vfwprintf_s.c
+++ b/src/wchar/vfwprintf_s.c
@@ -80,6 +80,7 @@ EXPORT int vfwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt,
                        va_list ap) {
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(stream == NULL)) {
         invoke_safe_str_constraint_handler("vfwprintf_s: stream is null", NULL,
@@ -115,6 +116,7 @@ EXPORT int vfwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vfwprintf(stream, fmt, ap);
 
@@ -123,6 +125,8 @@ EXPORT int vfwprintf_s(FILE *restrict stream, const wchar_t *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vfwscanf_s.c b/src/wchar/vfwscanf_s.c
index d3e36122..8fde2666 100644
--- a/src/wchar/vfwscanf_s.c
+++ b/src/wchar/vfwscanf_s.c
@@ -92,6 +92,7 @@ EXPORT int vfwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt,
 {
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(stream == NULL)) {
         invoke_safe_str_constraint_handler("vfwscanf_s: stream is null", NULL,
@@ -108,7 +109,7 @@ EXPORT int vfwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt,
     }
 #ifdef HAVE_MINGW32
     if (unlikely(!*fmt)) {
-        errno = 0;
+        // errno = 0;
         return EOF;
     }
 #endif
@@ -137,6 +138,7 @@ EXPORT int vfwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vfwscanf(stream, fmt, ap);
 
@@ -146,6 +148,8 @@ EXPORT int vfwscanf_s(FILE *restrict stream, const wchar_t *restrict fmt,
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
         /* TODO: zero the out args */
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vsnwprintf_s.c b/src/wchar/vsnwprintf_s.c
index 99e153b3..0d353fc3 100644
--- a/src/wchar/vsnwprintf_s.c
+++ b/src/wchar/vsnwprintf_s.c
@@ -127,6 +127,7 @@ EXPORT int _vsnwprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
 #ifndef HAVE_VSNWPRINTF_S
     va_list ap2;
 #endif
+    int l_errno;
 
     if (unlikely(dest == NULL)) {
         invoke_safe_str_constraint_handler("vsnwprintf_s: dest is null", NULL,
@@ -187,6 +188,7 @@ EXPORT int _vsnwprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     /* C11 solves the ESNOSPC problem */
 #ifdef HAVE_VSNWPRINTF_S
@@ -201,6 +203,8 @@ EXPORT int _vsnwprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
             static wchar_t tmp[512];
             if (unlikely(dmax == 1)) {
                 *dest = L'\0';
+                if (0 == errno)
+                    errno = l_errno;
                 return 1;
             }
             ret = vswprintf(tmp, 512, fmt, ap2);
@@ -233,6 +237,8 @@ EXPORT int _vsnwprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
         return ret;
     }
 #endif
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vswprintf_s.c b/src/wchar/vswprintf_s.c
index e1546239..e0fb25fc 100644
--- a/src/wchar/vswprintf_s.c
+++ b/src/wchar/vswprintf_s.c
@@ -112,6 +112,7 @@ EXPORT int _vswprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
 {
     wchar_t *p;
     int ret = -1;
+    int l_errno;
     const size_t destsz = dmax * sizeof(wchar_t);
 #ifndef HAVE_VSNWPRINTF_S
     va_list ap2;
@@ -171,6 +172,7 @@ EXPORT int _vswprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     /* C11 solves the ESNOSPC problem */
 #ifdef HAVE_VSNWPRINTF_S
@@ -195,7 +197,7 @@ EXPORT int _vswprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
         }
         if (ret > 0) {
         nospc:
-            errno = 0;
+            // errno = 0;
             handle_werror(dest, dmax, "vswprintf_s: len exceeds dmax", ESNOSPC);
             return -(ESNOSPC);
         }
@@ -212,6 +214,8 @@ EXPORT int _vswprintf_s_chk(wchar_t *restrict dest, rsize_t dmax,
 #endif
         *dest = 0;
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vswscanf_s.c b/src/wchar/vswscanf_s.c
index 8128f6ec..4e2d4c84 100644
--- a/src/wchar/vswscanf_s.c
+++ b/src/wchar/vswscanf_s.c
@@ -88,6 +88,7 @@ EXPORT int vswscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
                       va_list ap) {
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(src == NULL)) {
         invoke_safe_str_constraint_handler("vswscanf_s: src is null", NULL,
@@ -132,6 +133,7 @@ EXPORT int vswscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vswscanf(src, fmt, ap);
 
@@ -140,6 +142,8 @@ EXPORT int vswscanf_s(const wchar_t *restrict src, const wchar_t *restrict fmt,
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, (void *)src, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vwprintf_s.c b/src/wchar/vwprintf_s.c
index 54362cf6..ddd824f8 100644
--- a/src/wchar/vwprintf_s.c
+++ b/src/wchar/vwprintf_s.c
@@ -75,6 +75,7 @@ any of the arguments corresponding to %s is a null pointer
 EXPORT int vwprintf_s(const wchar_t *restrict fmt, va_list ap) {
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(fmt == NULL)) {
         invoke_safe_str_constraint_handler("vwprintf_s: fmt is null", NULL,
@@ -104,6 +105,7 @@ EXPORT int vwprintf_s(const wchar_t *restrict fmt, va_list ap) {
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vwprintf(fmt, ap);
 
@@ -112,6 +114,8 @@ EXPORT int vwprintf_s(const wchar_t *restrict fmt, va_list ap) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, -ret);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/vwscanf_s.c b/src/wchar/vwscanf_s.c
index 57d502ff..3646ea7f 100644
--- a/src/wchar/vwscanf_s.c
+++ b/src/wchar/vwscanf_s.c
@@ -87,6 +87,7 @@ EXPORT int vwscanf_s(const wchar_t *restrict fmt, va_list ap)
 {
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(fmt == NULL)) {
         invoke_safe_str_constraint_handler("vwscanf_s: fmt is null", NULL,
@@ -124,6 +125,7 @@ EXPORT int vwscanf_s(const wchar_t *restrict fmt, va_list ap)
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     ret = vwscanf(fmt, ap);
 
@@ -132,6 +134,8 @@ EXPORT int vwscanf_s(const wchar_t *restrict fmt, va_list ap)
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }
diff --git a/src/wchar/wcstok_s.c b/src/wchar/wcstok_s.c
index e26d6611..a17335c4 100644
--- a/src/wchar/wcstok_s.c
+++ b/src/wchar/wcstok_s.c
@@ -189,6 +189,7 @@ EXPORT wchar_t *_wcstok_s_chk(wchar_t *restrict dest, rsize_t *restrict dmaxp,
     rsize_t slen;
     rsize_t destsz;
     const wchar_t *orig_dest = dest;
+    int l_errno;
 
     if (unlikely(dmaxp == NULL)) {
         invoke_safe_str_constraint_handler("wcstok_s: dmaxp is NULL",
@@ -264,6 +265,7 @@ EXPORT wchar_t *_wcstok_s_chk(wchar_t *restrict dest, rsize_t *restrict dmaxp,
      * scan dest for a delimiter
      */
     ptoken = NULL;
+    l_errno = errno;
     errno = 0;
     while (*dest != L'\0' && !ptoken) {
 
@@ -314,6 +316,8 @@ EXPORT wchar_t *_wcstok_s_chk(wchar_t *restrict dest, rsize_t *restrict dmaxp,
      */
     if (ptoken == NULL) {
         *dmaxp = dlen;
+        if (0 == errno)
+            errno = l_errno;
         return (ptoken);
     }
 
@@ -367,6 +371,8 @@ EXPORT wchar_t *_wcstok_s_chk(wchar_t *restrict dest, rsize_t *restrict dmaxp,
         dlen--;
     }
 
+    if (0 == errno)
+        errno = l_errno;
     *dmaxp = dlen;
     return (ptoken);
 }
diff --git a/src/wchar/wscanf_s.c b/src/wchar/wscanf_s.c
index 7ab446dc..0df9a26a 100644
--- a/src/wchar/wscanf_s.c
+++ b/src/wchar/wscanf_s.c
@@ -89,6 +89,7 @@ EXPORT int wscanf_s(const wchar_t *restrict fmt, ...) {
     va_list ap;
     wchar_t *p;
     int ret;
+    int l_errno;
 
     if (unlikely(fmt == NULL)) {
         invoke_safe_str_constraint_handler("wscanf_s: fmt is null", NULL,
@@ -121,6 +122,7 @@ EXPORT int wscanf_s(const wchar_t *restrict fmt, ...) {
 #error need wcsstr or wcschr
 #endif
 
+    l_errno = errno;
     errno = 0;
     va_start(ap, fmt);
     ret = vwscanf(fmt, ap);
@@ -131,6 +133,8 @@ EXPORT int wscanf_s(const wchar_t *restrict fmt, ...) {
         strcat(errstr, strerror(errno));
         invoke_safe_str_constraint_handler(errstr, NULL, errno);
     }
+    if (0 == errno)
+        errno = l_errno;
 
     return ret;
 }