diff --git a/format.h b/format.h
index a98a1660..45d54283 100644
--- a/format.h
+++ b/format.h
@@ -976,6 +976,7 @@ template <typename T>
 T &get();
 
 struct DummyStream : std::ostream {
+  DummyStream();  // Suppress a bogus warning in MSVC.
   // Hide all operator<< overloads from std::ostream.
   void operator<<(Null<>);
 };