diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 718a405..ad97c0d 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -19,9 +19,9 @@ static __attribute__((unused))
 int memcmp(const void *s1, const void *s2, size_t n)
 {
 	size_t ofs = 0;
-	char c1 = 0;
+	int c1 = 0;
 
-	while (ofs < n && !(c1 = ((char *)s1)[ofs] - ((char *)s2)[ofs])) {
+	while (ofs < n && !(c1 = ((unsigned char *)s1)[ofs] - ((unsigned char *)s2)[ofs])) {
 		ofs++;
 	}
 	return c1;