diff --git a/icu4c/source/common/unicode/utf16cppiter.h b/icu4c/source/common/unicode/utf16cppiter.h
index 777cea6174e4..bcb7221fd5b3 100644
--- a/icu4c/source/common/unicode/utf16cppiter.h
+++ b/icu4c/source/common/unicode/utf16cppiter.h
@@ -169,6 +169,15 @@ class U16IteratorBase {
     // @internal
     bool operator!=(const U16IteratorBase &other) const { return !operator==(other); }
 
+    // @internal
+    void dec() {
+        // TODO: assert current != limit -- more precisely: start <= current < limit
+        // Very similar to U16_BACK_1().
+        if (U16_IS_TRAIL(*(--current)) && current != start && U16_IS_LEAD(*(current - 1))) {
+            --current;
+        }
+    }
+
     // @internal
     CodeUnits<Unit16, CP32> readAndInc(const Unit16 *&p) const {
         // TODO: assert p != limit -- more precisely: start <= p < limit
@@ -410,6 +419,14 @@ class U16UnsafeIteratorBase {
     // @internal
     bool operator!=(const U16UnsafeIteratorBase &other) const { return !operator==(other); }
 
+    // @internal
+    void dec() {
+        // Very similar to U16_BACK_1_UNSAFE().
+        if (U16_IS_TRAIL(*(--current))) {
+            --current;
+        }
+    }
+
     // @internal
     UnsafeCodeUnits<Unit16, CP32> readAndInc(const Unit16 *&p) const {
         // Very similar to U16_NEXT_UNSAFE().