diff --git a/json_object.c b/json_object.c
index d59a317..1e4f86d 100644
--- a/json_object.c
+++ b/json_object.c
@@ -180,8 +180,9 @@ static int json_escape_str(struct printbuf *pb, const char *str, size_t len, int
 {
 	size_t pos = 0, start_offset = 0;
 	unsigned char c;
-	while (len--)
+	while (len)
 	{
+		--len;
 		c = str[pos];
 		switch (c)
 		{