diff --git a/include/wx/wxcrtbase.h b/include/wx/wxcrtbase.h
index a48756a431..f7c77daeb7 100644
--- a/include/wx/wxcrtbase.h
+++ b/include/wx/wxcrtbase.h
@@ -664,12 +664,24 @@ WXDLLIMPEXP_BASE size_t wxCRT_StrftimeW(wchar_t *s, size_t max,
 /* safe version of strlen() (returns 0 if passed NULL pointer) */
 inline size_t wxStrlen(const char *s) { return s ? wxCRT_StrlenA(s) : 0; }
 inline size_t wxStrlen(const wchar_t *s) { return s ? wxCRT_StrlenW(s) : 0; }
+#ifndef wxWCHAR_T_IS_WXCHAR16
+       size_t wxStrlen(const wxChar16 *s );
+#endif
+#ifndef wxWCHAR_T_IS_WXCHAR32
+       size_t wxStrlen(const wxChar32 *s );
+#endif
 #define wxWcslen wxCRT_StrlenW
 
 #define wxStrdupA wxCRT_StrdupA
 #define wxStrdupW wxCRT_StrdupW
 inline char* wxStrdup(const char *s) { return wxCRT_StrdupA(s); }
 inline wchar_t* wxStrdup(const wchar_t *s) { return wxCRT_StrdupW(s); }
+#ifndef wxWCHAR_T_IS_WXCHAR16
+       wxChar16* wxStrdup(const wxChar16* s);
+#endif
+#ifndef wxWCHAR_T_IS_WXCHAR32
+       wxChar32* wxStrdup(const wxChar32* s);
+#endif
 
 #endif /* __cplusplus */