diff --git a/src/microhttpd/connection.c b/src/microhttpd/connection.c
index 3e6a4ba0..925f9df5 100644
--- a/src/microhttpd/connection.c
+++ b/src/microhttpd/connection.c
@@ -1980,6 +1980,8 @@ build_header_response (struct MHD_Connection *connection)
   buf = c->write_buffer;
   pos = c->write_buffer_append_offset;
   buf_size = c->write_buffer_size;
+  if ((NULL == buf) || (0 == buf_size))
+    return MHD_NO;
 
   /* * The status line * */