--- a/gfx/2d/Blur.cpp
+++ b/gfx/2d/Blur.cpp
@@ -4,22 +4,19 @@
 
 #include "mozilla/gfx/Blur.h"
 
 #include <algorithm>
 #include <math.h>
 #include <string.h>
 
 #include "mozilla/CheckedInt.h"
+#include "mozilla/Constants.h"
 #include "mozilla/Util.h"
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 using namespace std;
 
 namespace mozilla {
 namespace gfx {
 
 /**
  * Box blur involves looking at one pixel, and setting its value to the average
  * of its neighbouring pixels.

--- a/gfx/2d/DrawTargetD2D.cpp
+++ b/gfx/2d/DrawTargetD2D.cpp
@@ -9,23 +9,20 @@
 #include "ShadersD2D.h"
 #include "PathD2D.h"
 #include "GradientStopsD2D.h"
 #include "ScaledFontDWrite.h"
 #include "ImageScaling.h"
 #include "Logging.h"
 #include "Tools.h"
 #include <algorithm>
+#include "mozilla/Constants.h"
 
 #include <dwrite.h>
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 typedef HRESULT (WINAPI*D2D1CreateFactoryFunc)(
     D2D1_FACTORY_TYPE factoryType,
     REFIID iid,
     CONST D2D1_FACTORY_OPTIONS *pFactoryOptions,
     void **factory
 );
 
 typedef HRESULT (WINAPI*D3D10CreateEffectFromMemoryFunc)(

--- a/gfx/2d/PathD2D.cpp
+++ b/gfx/2d/PathD2D.cpp
@@ -3,20 +3,17 @@
  * 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/. */
 
 #include "PathD2D.h"
 #include "HelpersD2D.h"
 #include <math.h>
 #include "DrawTargetD2D.h"
 #include "Logging.h"
-
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
+#include "mozilla/Constants.h"
 
 namespace mozilla {
 namespace gfx {
 
 // This class exists as a wrapper for ID2D1SimplifiedGeometry sink, it allows
 // a geometry to be duplicated into a geometry sink, while removing the final
 // figure end and thus allowing a figure that was implicitly closed to be
 // continued.

--- a/gfx/2d/PathHelpers.h
+++ b/gfx/2d/PathHelpers.h
@@ -2,20 +2,17 @@
  * 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_PATHHELPERS_H_
 #define MOZILLA_GFX_PATHHELPERS_H_
 
 #include "2D.h"
-
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
+#include "mozilla/Constants.h"
 
 namespace mozilla {
 namespace gfx {
 
 template <typename T>
 void ArcToBezier(T* aSink, const Point &aOrigin, float aRadius, float aStartAngle,
                  float aEndAngle, bool aAntiClockwise)
 {

--- a/gfx/layers/ipc/AsyncPanZoomController.cpp
+++ b/gfx/layers/ipc/AsyncPanZoomController.cpp
@@ -1,32 +1,29 @@
 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set sw=4 ts=8 et tw=80 : */
 /* 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/. */
 
 #include "CompositorParent.h"
 #include "mozilla/gfx/2D.h"
+#include "mozilla/Constants.h"
 #include "mozilla/Util.h"
 #include "mozilla/XPCOM.h"
 #include "mozilla/Monitor.h"
 #include "AsyncPanZoomController.h"
 #include "GestureEventListener.h"
 #include "nsIThreadManager.h"
 #include "nsThreadUtils.h"
 #include "Layers.h"
 
 namespace mozilla {
 namespace layers {
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 static const float EPSILON = 0.0001;
 
 /**
  * Maximum amount of time while panning before sending a viewport change. This
  * will asynchronously repaint the page. It is also forced when panning stops.
  */
 static const PRInt32 PAN_REPAINT_INTERVAL = 250;
 

--- a/gfx/thebes/gfxContext.cpp
+++ b/gfx/thebes/gfxContext.cpp
@@ -3,19 +3,17 @@
  * 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/. */
 
 #ifdef _MSC_VER
 #define _USE_MATH_DEFINES
 #endif
 #include <math.h>
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
+#include "mozilla/Constants.h"
 
 #include "cairo.h"
 
 #include "gfxContext.h"
 
 #include "gfxColor.h"
 #include "gfxMatrix.h"
 #include "gfxASurface.h"

--- a/js/src/jsmath.cpp
+++ b/js/src/jsmath.cpp
@@ -3,16 +3,17 @@
  * 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/. */
 
 /*
  * JS math package.
  */
 
+#include "mozilla/Constants.h"
 #include "mozilla/FloatingPoint.h"
 
 #include <stdlib.h>
 #include "jstypes.h"
 #include "prmjtime.h"
 #include "jsapi.h"
 #include "jsatom.h"
 #include "jscntxt.h"
@@ -38,19 +39,16 @@ using namespace js;
 #define M_LOG10E        0.43429448190325182765
 #endif
 #ifndef M_LN2
 #define M_LN2           0.69314718055994530942
 #endif
 #ifndef M_LN10
 #define M_LN10          2.30258509299404568402
 #endif
-#ifndef M_PI
-#define M_PI            3.14159265358979323846
-#endif
 #ifndef M_SQRT2
 #define M_SQRT2         1.41421356237309504880
 #endif
 #ifndef M_SQRT1_2
 #define M_SQRT1_2       0.70710678118654752440
 #endif
 
 static JSConstDoubleSpec math_constants[] = {

--- a/layout/svg/base/src/nsSVGUtils.h
+++ b/layout/svg/base/src/nsSVGUtils.h
@@ -17,16 +17,17 @@
 #include "nsChangeHint.h"
 #include "nsColor.h"
 #include "nsCOMPtr.h"
 #include "nsID.h"
 #include "nsISupportsBase.h"
 #include "nsMathUtils.h"
 #include "nsPoint.h"
 #include "nsRect.h"
+#include "mozilla/Constants.h"
 
 class gfxASurface;
 class gfxContext;
 class gfxImageSurface;
 class gfxPattern;
 class nsFrameList;
 class nsIContent;
 class nsIDocument;
@@ -51,20 +52,16 @@ struct nsStyleSVGPaint;
 namespace mozilla {
 class SVGAnimatedPreserveAspectRatio;
 class SVGPreserveAspectRatio;
 namespace dom {
 class Element;
 } // namespace dom
 } // namespace mozilla
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 // SVG Frame state bits
 #define NS_STATE_IS_OUTER_SVG                    NS_FRAME_STATE_BIT(20)
 
 /* are we the child of a non-display container? */
 #define NS_STATE_SVG_NONDISPLAY_CHILD            NS_FRAME_STATE_BIT(22)
 
 // If this bit is set, we are a <clipPath> element or descendant.
 #define NS_STATE_SVG_CLIPPATH_CHILD              NS_FRAME_STATE_BIT(23)

new file mode 100644
--- /dev/null
+++ b/mfbt/Constants.h
@@ -0,0 +1,15 @@
+/* -*- 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/. */
+
+/* mfbt math constants. */
+
+#ifndef mozilla_Constants_h_
+#define mozilla_Constants_h_
+
+#ifndef M_PI
+#  define M_PI 3.14159265358979323846
+#endif
+
+#endif  /* mozilla_Constants_h_ */

--- a/mfbt/exported_headers.mk
+++ b/mfbt/exported_headers.mk
@@ -8,16 +8,17 @@
 
 EXPORTS_NAMESPACES += mozilla
 
 EXPORTS_mozilla += \
   Assertions.h \
   Attributes.h \
   BloomFilter.h \
   CheckedInt.h \
+  Constants.h \
   FloatingPoint.h \
   GuardObjects.h \
   HashFunctions.h \
   Likely.h \
   LinkedList.h \
   MSStdInt.h \
   RangedPtr.h \
   RefPtr.h \

--- a/widget/windows/nsWinGesture.cpp
+++ b/widget/windows/nsWinGesture.cpp
@@ -7,24 +7,21 @@
  * nsWinGesture - Touch input handling for tablet displays.
  */
 
 #include "nscore.h"
 #include "nsWinGesture.h"
 #include "nsUXThemeData.h"
 #include "nsIDOMSimpleGestureEvent.h"
 #include "nsGUIEvent.h"
+#include "mozilla/Constants.h"
 #include "mozilla/Preferences.h"
 
 using namespace mozilla;
 
-#ifndef M_PI
-#define M_PI 3.14159265358979323846
-#endif
-
 #ifdef PR_LOGGING
 extern PRLogModuleInfo* gWindowsLog;
 #endif
 
 const PRUnichar nsWinGesture::kGestureLibraryName[] =  L"user32.dll";
 HMODULE nsWinGesture::sLibraryHandle = nullptr;
 nsWinGesture::GetGestureInfoPtr nsWinGesture::getGestureInfo = nullptr;
 nsWinGesture::CloseGestureInfoHandlePtr nsWinGesture::closeGestureInfoHandle = nullptr;