diff --git a/src/string/strncmp.c b/src/string/strncmp.c
index 0469f47..d03448a 100644
--- a/src/string/strncmp.c
+++ b/src/string/strncmp.c
@@ -7,5 +7,5 @@ int strncmp(const char *s1, const char *s2, size_t n)
 	size_t i = -1;
 	while (++i < n - 1 && s1[i] != '\0' && s2[i] != '\0'
 	       && s1[i] == s2[i]) ;
-	return (s1[i] - s2[i]);
+	return ((unsigned char) s1[i] - (unsigned char) s2[i]);
 }