diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 583287f42..252e73a91 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -161,11 +161,11 @@ const char* getprogname(void) __INTRODUCED_IN(21);
 void setprogname(const char* __name) __INTRODUCED_IN(21);
 
 int mblen(const char* __s, size_t __n) __INTRODUCED_IN_NO_GUARD_FOR_NDK(26);
-size_t mbstowcs(wchar_t* __dst, const char* __src, size_t __n);
+size_t mbstowcs(wchar_t* __dst, const char* __src, size_t __n) __INTRODUCED_IN(21) __VERSIONER_NO_GUARD;
 int mbtowc(wchar_t* __wc_ptr, const char* __s, size_t __n) __INTRODUCED_IN_NO_GUARD_FOR_NDK(21);
 int wctomb(char* __dst, wchar_t __wc) __INTRODUCED_IN_NO_GUARD_FOR_NDK(21);
 
-size_t wcstombs(char* __dst, const wchar_t* __src, size_t __n);
+size_t wcstombs(char* __dst, const wchar_t* __src, size_t __n) __INTRODUCED_IN(21) __VERSIONER_NO_GUARD;
 
 #if __ANDROID_API__ >= 21
 size_t __ctype_get_mb_cur_max(void) __INTRODUCED_IN(21);
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index 00b25d395..7397b687c 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -631,7 +631,7 @@ LIBC {
     mbsinit;
     mbsnrtowcs; # introduced=21
     mbsrtowcs;
-    mbstowcs;
+    mbstowcs; # introduced=21
     mbtowc; # introduced=21
     memalign;
     memccpy;
@@ -1194,7 +1194,7 @@ LIBC {
     wcstold_l; # introduced=21
     wcstoll; # introduced=21
     wcstoll_l; # introduced=21
-    wcstombs;
+    wcstombs; # introduced=21
     wcstoul;
     wcstoull; # introduced=21
     wcstoull_l; # introduced=21