diff --git a/cJSON.c b/cJSON.c
index f6dd11c..8f44a50 100644
--- a/cJSON.c
+++ b/cJSON.c
@@ -778,7 +778,7 @@ static cJSON_bool parse_string(cJSON * const item, parse_buffer * const input_bu
     unsigned char *output = NULL;
 
     /* not a string */
-    if (buffer_at_offset(input_buffer)[0] != '\"')
+    if (cannot_access_at_index(input_buffer, 0) || buffer_at_offset(input_buffer)[0] != '\"')
     {
         goto fail;
     }