diff --git a/flexdll.c b/flexdll.c
index c98fe6a..a295ffd 100644
--- a/flexdll.c
+++ b/flexdll.c
@@ -584,7 +584,7 @@ void *flexdll_dlsym(void *u, const char *name) {
   err = get_tls_error(TLS_ERROR_NOP);
   if (err == NULL) return NULL;
 
-  if (WaitForSingleObject(units_mutex, INFINITE) == WAIT_FAILED) {
+  if (WaitForSingleObject(units_mutex, INFINITE) == WAIT_OBJECT_0) {
     if (!err->code) err->code = 1;
     return NULL;
   }