diff --git a/winsup/cygwin/local_includes/wchar.h b/winsup/cygwin/local_includes/wchar.h
index 3d746c29b..10b44791c 100644
--- a/winsup/cygwin/local_includes/wchar.h
+++ b/winsup/cygwin/local_includes/wchar.h
@@ -41,7 +41,7 @@ extern wctomb_f __utf8_wctomb;
 
 /* replacement function for mbrtowc, returning a wint_t representing
    a UTF-32 value. Defined in strfuncs.cc */
-extern wint_t mbrtowi (wint_t *, const char *, size_t, mbstate_t *);
+extern size_t mbrtowi (wint_t *, const char *, size_t, mbstate_t *);
 
 #ifdef __cplusplus
 }
diff --git a/winsup/cygwin/strfuncs.cc b/winsup/cygwin/strfuncs.cc
index 0b9d8ac1f..d62179a1d 100644
--- a/winsup/cygwin/strfuncs.cc
+++ b/winsup/cygwin/strfuncs.cc
@@ -114,7 +114,7 @@ transform_chars_af_unix (PWCHAR out, const char *path, __socklen_t len)
 
 /* replacement function for mbrtowc, returning a wint_t representing
    a UTF-32 value. */
-extern "C" wint_t
+extern "C" size_t
 mbrtowi (wint_t *pwi, const char *s, size_t n, mbstate_t *ps)
 {
   size_t len, len2;