--- a/gfx/2d/BaseSize.h
+++ b/gfx/2d/BaseSize.h
@@ -2,16 +2,18 @@
  * This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef MOZILLA_GFX_BASESIZE_H_
 #define MOZILLA_GFX_BASESIZE_H_
 
 #include <algorithm>
+#include <ostream>
+
 #include "mozilla/Attributes.h"
 
 namespace mozilla {
 namespace gfx {
 
 /**
  * Do not use this class directly. Subclass it, pass that subclass as the
  * Sub parameter, and only use that subclass. This allows methods to safely
@@ -98,14 +100,19 @@ struct BaseSize {
     return Sub(std::min(aA.width, aB.width),
                std::min(aA.height, aB.height));
   }
 
   friend Sub Max(const Sub& aA, const Sub& aB) {
     return Sub(std::max(aA.width, aB.width),
                std::max(aA.height, aB.height));
   }
+
+  friend std::ostream& operator<<(std::ostream& aStream,
+      const BaseSize<T, Sub>& aSize) {
+    return aStream << aSize.width << " x " << aSize.height;
+  }
 };
 
 } // namespace gfx
 } // namespace mozilla
 
 #endif /* MOZILLA_GFX_BASESIZE_H_ */