diff --git a/json_pointer.c b/json_pointer.c
index 380d6e52f8..d106e9e9ca 100644
--- a/json_pointer.c
+++ b/json_pointer.c
@@ -43,7 +43,7 @@ static int is_valid_index(struct json_object *jo, const char *path, int32_t *idx
 	/* this code-path optimizes a bit, for when we reference the 0-9 index range in a JSON array
 	   and because leading zeros not allowed */
 	if (len == 1) {
-		if (isdigit(path[0])) {
+		if (isdigit((int)path[0])) {
 			*idx = (path[0] - '0');
 			goto check_oob;
 		}
@@ -57,7 +57,7 @@ static int is_valid_index(struct json_object *jo, const char *path, int32_t *idx
 	}
 	/* RFC states base-10 decimals */
 	for (i = 0; i < len; i++) {
-		if (!isdigit(path[i])) {
+		if (!isdigit((int)path[i])) {
 			errno = EINVAL;
 			return 0;
 		}