diff --git a/src/test-serialize.cc b/src/test-serialize.cc
index 954d62dde..1238c3508 100644
--- a/src/test-serialize.cc
+++ b/src/test-serialize.cc
@@ -44,7 +44,7 @@ main (int argc, char **argv)
   s.end_serialize ();
 
   hb_bytes_t bytes = s.copy_bytes ();
-  printf ("serialized %u bytes\n", bytes.length);
+  assert (bytes.length == 10);
   bytes.fini ();
 
   return 0;