diff --git a/gfx/2d/QuartzSupport.h b/gfx/2d/QuartzSupport.h
index 644a4dfb521..558a64fca92 100644
--- a/gfx/2d/QuartzSupport.h
+++ b/gfx/2d/QuartzSupport.h
@@ -87,8 +87,8 @@ private:
   mozilla::RefPtr<MacIOSurface> mIOSurface;
   uint32_t                  mFBO;
   uint32_t                  mIOTexture;
-  uint32_t                  mUnsupportedWidth;
-  uint32_t                  mUnsupportedHeight;
+  int                       mUnsupportedWidth;
+  int                       mUnsupportedHeight;
   AllowOfflineRendererEnum  mAllowOfflineRenderer;
   double                    mContentsScaleFactor;
 };
diff --git a/gfx/2d/QuartzSupport.mm b/gfx/2d/QuartzSupport.mm
index d64b9fac020..c83f50e0170 100644
--- a/gfx/2d/QuartzSupport.mm
+++ b/gfx/2d/QuartzSupport.mm
@@ -807,7 +807,8 @@ void nsCARenderer::AttachIOSurface(RefPtr<MacIOSurface> aSurface) {
     // Rebind the FBO to make it live
     ::glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, mFBO);
 
-    if (mIOSurface->GetWidth() != width || mIOSurface->GetHeight() != height) {
+    if (static_cast<int>(mIOSurface->GetWidth()) != width ||
+        static_cast<int>(mIOSurface->GetHeight()) != height) {
       width = mIOSurface->GetWidth();
       height = mIOSurface->GetHeight();
       SetBounds(width, height);