diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index bca74bad0d27..cdb178d2d545 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -1081,7 +1081,7 @@ NS_INTERFACE_MAP_END
 
 
 // Initialize our static variables.
-uint32_t CanvasRenderingContext2D::sNumLivingContexts = 0;
+uintptr_t CanvasRenderingContext2D::sNumLivingContexts = 0;
 DrawTarget* CanvasRenderingContext2D::sErrorTarget = nullptr;
 static bool sMaxContextsInitialized = false;
 static int32_t sMaxContexts = 0;
diff --git a/dom/canvas/CanvasRenderingContext2D.h b/dom/canvas/CanvasRenderingContext2D.h
index 870599c48038..c0402515e09d 100644
--- a/dom/canvas/CanvasRenderingContext2D.h
+++ b/dom/canvas/CanvasRenderingContext2D.h
@@ -578,7 +578,7 @@ protected:
     * The number of living nsCanvasRenderingContexts.  When this goes down to
     * 0, we free the premultiply and unpremultiply tables, if they exist.
     */
-  static uint32_t sNumLivingContexts;
+  static uintptr_t sNumLivingContexts;
 
   static mozilla::gfx::DrawTarget* sErrorTarget;