diff --git a/sdk/include/crt/string.h b/sdk/include/crt/string.h
index 3249254c947..caeb23fcdc9 100644
--- a/sdk/include/crt/string.h
+++ b/sdk/include/crt/string.h
@@ -150,6 +150,7 @@ extern "C" {
     _In_z_ const char *_Str1,
     _In_z_ const char *_Str2);
 
+  _CRTIMP
   size_t
   __cdecl
   strlen(
diff --git a/sdk/include/crt/wchar.h b/sdk/include/crt/wchar.h
index eadde09cfbd..309bed76cef 100644
--- a/sdk/include/crt/wchar.h
+++ b/sdk/include/crt/wchar.h
@@ -1929,6 +1929,7 @@ _CRTIMP int __cdecl iswblank(wint_t _C);
     _In_z_ const wchar_t *_Str,
     _In_z_ const wchar_t *_Control);
 
+  _CRTIMP
   size_t
   __cdecl
   wcslen(