diff --git a/lib/stdlib/mem.c b/lib/stdlib/mem.c
index f1f335a..ef33dba 100644
--- a/lib/stdlib/mem.c
+++ b/lib/stdlib/mem.c
@@ -48,10 +48,10 @@
  */
 int memcmp(const void *s1, const void *s2, size_t len)
 {
-	const char *s = s1;
-	const char *d = s2;
-	char dc;
-	char sc;
+	const unsigned char *s = s1;
+	const unsigned char *d = s2;
+	unsigned char sc;
+	unsigned char dc;
 
 	while (len--) {
 		sc = *s++;