diff --git a/ext/standard/string.c b/ext/standard/string.c
index 452fc4761eb..28f33c519a5 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -1315,9 +1315,9 @@ PHPAPI void php_stripcslashes(char *str, int *len)
 				case 'b': *target++='\b'; nlen--; break;
 				case 'f': *target++='\f'; nlen--; break;
 				case '\\': *target++='\\'; nlen--; break;
-				case 'x': if (source+1<end && isxdigit(*(source+1))) {
+				case 'x': if (source+1<end && isxdigit((int)(*(source+1)))) {
 						numtmp[0] = *++source;
-						if (source+1<end && isxdigit(*(source+1))) {
+						if (source+1<end && isxdigit((int)(*(source+1)))) {
 							numtmp[1] = *++source;
 							numtmp[2] = '\0';
 							nlen-=3;