diff --git a/lib/string.c b/lib/string.c
index 7548eb715ddb..77bd0b1d3296 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -977,7 +977,7 @@ void *memscan(void *addr, int c, size_t size)
 	unsigned char *p = addr;
 
 	while (size) {
-		if (*p == c)
+		if (*p == (unsigned char)c)
 			return (void *)p;
 		p++;
 		size--;