diff --git a/test_utils.h b/test_utils.h
index cd17ec1..bba3ed1 100644
--- a/test_utils.h
+++ b/test_utils.h
@@ -44,6 +44,8 @@
   return system(cmd.c_str());
 }
 
+void FillWithData(std::vector<char>* buffer);
+
 namespace {
 // 300 byte pseudo-random string. Not null terminated.
 // This does not gzip compress well.