diff --git a/json_object.c b/json_object.c
index 7f085f3..4c4d04b 100644
--- a/json_object.c
+++ b/json_object.c
@@ -110,7 +110,7 @@ static int json_escape_str(struct printbuf *pb, const char *str, int len)
 {
 	int pos = 0, start_offset = 0;
 	unsigned char c;
-	while (len--)
+	while (pos < len)
 	{
 		c = str[pos];
 		switch(c)