--- a/gfx/thebes/gfxBlur.cpp
+++ b/gfx/thebes/gfxBlur.cpp
@@ -429,16 +429,21 @@ CreateBlurMask(const IntSize& aRectSize,
 
 static already_AddRefed<SourceSurface>
 CreateBoxShadow(DrawTarget& aDT, SourceSurface* aBlurMask, const gfxRGBA& aShadowColor)
 {
   IntSize blurredSize = aBlurMask->GetSize();
   gfxPlatform* platform = gfxPlatform::GetPlatform();
   RefPtr<DrawTarget> boxShadowDT =
     platform->CreateOffscreenContentDrawTarget(blurredSize, SurfaceFormat::B8G8R8A8);
+
+  if (!boxShadowDT) {
+    return nullptr;
+  }
+
   MOZ_ASSERT(boxShadowDT->GetType() == aDT.GetType());
 
   ColorPattern shadowColor(ToDeviceColor(aShadowColor));
   boxShadowDT->MaskSurface(shadowColor, aBlurMask, Point(0, 0));
   return boxShadowDT->Snapshot();
 }
 
 SourceSurface*
@@ -470,16 +475,20 @@ GetBlur(DrawTarget& aDT,
   RefPtr<SourceSurface> blurMask =
     CreateBlurMask(aRectSize, aCornerRadii, aBlurRadius, aExtendDestBy, aSlice, aDT);
 
   if (!blurMask) {
     return nullptr;
   }
 
   RefPtr<SourceSurface> boxShadow = CreateBoxShadow(aDT, blurMask, aShadowColor);
+  if (!boxShadow) {
+    return nullptr;
+  }
+
   CacheBlur(aDT, minSize, aBlurRadius, aCornerRadii, aShadowColor, aExtendDestBy, boxShadow);
   return boxShadow;
 }
 
 void
 gfxAlphaBoxBlur::ShutdownBlurCache()
 {
   delete gBlurCache;