diff --git a/src/microhttpd/postprocessor.c b/src/microhttpd/postprocessor.c
index 5f258a6b..6e6bfbd1 100644
--- a/src/microhttpd/postprocessor.c
+++ b/src/microhttpd/postprocessor.c
@@ -532,7 +532,8 @@ post_process_urlencoded (struct MHD_PostProcessor *pp,
     mhd_assert (end_key >= start_key);
     key_len = (size_t) (end_key - start_key);
     mhd_assert (0 != key_len); /* it must be always non-zero here */
-    if (pp->buffer_pos + key_len >= pp->buffer_size)
+    if ( (pp->buffer_pos + key_len >= pp->buffer_size) ||
+         (pp->buffer_pos + key_len < pp->buffer_pos) )
     {
       pp->state = PP_Error;
       return MHD_NO;