1 files changed, 1 insertions, 1 deletions
diff --git a/yamltree.c b/yamltree.c
index 0cb16ed..25fd25e 100644
--- a/yamltree.c
+++ b/yamltree.c
@@ -102,7 +102,7 @@ static void yaml_propval_string(yaml_emitter_t *emitter, char *str, int len)
 
 	/* Make sure the entire string is in the lower 7-bit ascii range */
 	for (i = 0; i < len; i++)
-		assert(isascii(str[i]));
+		assert(isascii((unsigned char)str[i]));
 
 	yaml_scalar_event_initialize(&event, NULL,
 		(const yaml_char_t *)YAML_STR_TAG, (const yaml_char_t*)str,