diff --git a/src/tkc/wchar32.c b/src/tkc/wchar32.c
index b7790c369..fb90f0b92 100644
--- a/src/tkc/wchar32.c
+++ b/src/tkc/wchar32.c
@@ -500,5 +500,9 @@ wchar_t* wmemset(wchar_t* s, wchar_t c, size_t n) {
 int iswspace(wint_t ch) {
   return ch == ' ';
 }
+
+int towlower(wint_t ch) {
+  return tolower(ch);
+}
 #endif/*WITH_WCSXXX*/