diff --git a/common/mock_http_fetcher.h b/common/mock_http_fetcher.h
index ea5b83d..3d7859b 100644
--- a/common/mock_http_fetcher.h
+++ b/common/mock_http_fetcher.h
@@ -36,7 +36,7 @@
 // MockHttpFetcher will send a chunk of data down in each call to BeginTransfer
 // and Unpause. For the other chunks of data, a callback is put on the run
 // loop and when that's called, another chunk is sent down.
-const size_t kMockHttpFetcherChunkSize(65536);
+static constexpr size_t kMockHttpFetcherChunkSize(65536);
 
 class MockHttpFetcher : public HttpFetcher {
  public: