--- a/layout/generic/nsHTMLReflowState.h
+++ b/layout/generic/nsHTMLReflowState.h
@@ -1,17 +1,17 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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/. */
 
 /* struct containing the input to nsIFrame::Reflow */
 
-#ifndef nsHTMLReflowState_h___
-#define nsHTMLReflowState_h___
+#ifndef mozilla_nsHTMLReflowState_h
+#define mozilla_nsHTMLReflowState_h
 
 #include "nsMargin.h"
 #include "nsStyleCoord.h"
 #include "nsIFrame.h"
 #include "mozilla/Assertions.h"
 #include <algorithm>
 
 class nsPresContext;
@@ -89,16 +89,18 @@ typedef uint32_t  nsCSSFrameType;
 
 /**
  * A macro to extract the type. Masks off the 'replaced' bit-flag
  */
 #define NS_FRAME_GET_TYPE(_ft)                           \
   ((_ft) & ~(NS_CSS_FRAME_TYPE_REPLACED |                \
              NS_CSS_FRAME_TYPE_REPLACED_CONTAINS_BLOCK))
 
+namespace mozilla {
+
 // A base class of nsHTMLReflowState that computes only the padding,
 // border, and margin, since those values are needed more often.
 struct nsCSSOffsetState {
 public:
   typedef mozilla::WritingMode WritingMode;
   typedef mozilla::LogicalMargin LogicalMargin;
 
   // the frame being reflowed
@@ -965,10 +967,12 @@ protected:
   void CalculateBorderPaddingMargin(mozilla::LogicalAxis aAxis,
                                     nscoord aContainingBlockSize,
                                     nscoord* aInsideBoxSizing,
                                     nscoord* aOutsideBoxSizing) const;
 
   void CalculateBlockSideMargins(nsIAtom* aFrameType);
 };
 
-#endif /* nsHTMLReflowState_h___ */
+} // namespace mozilla
 
+#endif // mozilla_nsHTMLReflowState_h
+