diff --git a/rlutil.h b/rlutil.h
index 24b6322..4bae8b6 100644
--- a/rlutil.h
+++ b/rlutil.h
@@ -574,7 +574,7 @@ RLUTIL_INLINE void locate(int x, int y) {
 #ifdef __cplusplus
 RLUTIL_INLINE void setString(const RLUTIL_STRING_T & str_) {
 	const char * const str = str_.data();
-	unsigned int len = str_.size();
+	unsigned int len = static_cast<unsigned int>( str_.size() );
 #else // __cplusplus
 RLUTIL_INLINE void setString(RLUTIL_STRING_T str) {
 	unsigned int len = strlen(str);