diff --git a/http_fetcher_unittest.cc b/http_fetcher_unittest.cc
index 4fb8903..e6204d3 100644
--- a/http_fetcher_unittest.cc
+++ b/http_fetcher_unittest.cc
@@ -322,6 +322,8 @@
  private:
   static void TypeConstraint(T *a) {
     AnyHttpFetcherTest *b = a;
+    if (b == 0) // Silence compiler warning of unused variable.
+      *b = a;
   }
 };