diff --git a/gfx/layers/ipc/ShadowLayerUtilsGralloc.cpp b/gfx/layers/ipc/ShadowLayerUtilsGralloc.cpp
index 884d780bb148..73bbf11c52c5 100644
--- a/gfx/layers/ipc/ShadowLayerUtilsGralloc.cpp
+++ b/gfx/layers/ipc/ShadowLayerUtilsGralloc.cpp
@@ -172,6 +172,9 @@ PixelFormatForImageFormat(gfxImageFormat aFormat)
     return android::PIXEL_FORMAT_RGBX_8888;
   case gfxImageFormat::RGB16_565:
     return android::PIXEL_FORMAT_RGB_565;
+  case gfxImageFormat::A8:
+    NS_WARNING("gralloc does not support gfxImageFormat::A8");
+    return android::PIXEL_FORMAT_UNKNOWN;
   default:
     MOZ_CRASH("Unknown gralloc pixel format");
   }
@@ -430,6 +433,10 @@ ISurfaceAllocator::PlatformAllocSurfaceDescriptor(const gfx::IntSize& aSize,
   PGrallocBufferChild* gc;
   bool defaultRBSwap;
 
+  if (PixelFormatForContentType(aContent) == android::PIXEL_FORMAT_UNKNOWN) {
+    return false;
+  }
+
   if (aCaps & USING_GL_RENDERING_ONLY) {
     gc = AllocGrallocBuffer(aSize,
                             PixelFormatForContentType(aContent),