diff --git a/gfx/layers/basic/BasicLayers.cpp b/gfx/layers/basic/BasicLayers.cpp
index 004bff848e2..1ac88b7d3ee 100644
--- a/gfx/layers/basic/BasicLayers.cpp
+++ b/gfx/layers/basic/BasicLayers.cpp
@@ -910,6 +910,9 @@ BasicImageLayer::GetAndPaintCurrentImage(gfxContext* aContext,
     return nsnull;
   }
 
+  NS_ASSERTION(surface->GetContentType() != gfxASurface::CONTENT_ALPHA,
+               "Image layer has alpha image");
+
   nsRefPtr<gfxPattern> pat = new gfxPattern(surface);
   if (!pat) {
     return nsnull;
diff --git a/gfx/layers/d3d10/ImageLayerD3D10.cpp b/gfx/layers/d3d10/ImageLayerD3D10.cpp
index fb13993893e..34de24fb8fe 100644
--- a/gfx/layers/d3d10/ImageLayerD3D10.cpp
+++ b/gfx/layers/d3d10/ImageLayerD3D10.cpp
@@ -191,6 +191,10 @@ ImageLayerD3D10::RenderLayer()
   if (image->GetFormat() == Image::CAIRO_SURFACE || image->GetFormat() == Image::REMOTE_IMAGE_BITMAP ||
       image->GetFormat() == Image::REMOTE_IMAGE_DXGI_TEXTURE)
   {
+    NS_ASSERTION(image->GetFormat() != Image::CAIRO_SURFACE ||
+                 !static_cast<CairoImage*>(image)->mSurface ||
+                 static_cast<CairoImage*>(image)->mSurface->GetContentType() != gfxASurface::CONTENT_ALPHA,
+                 "Image layer has alpha image");
     bool hasAlpha = false;
 
     nsRefPtr<ID3D10ShaderResourceView> srView = GetImageSRView(image, hasAlpha, getter_AddRefs(keyedMutex));
diff --git a/gfx/layers/d3d9/ImageLayerD3D9.cpp b/gfx/layers/d3d9/ImageLayerD3D9.cpp
index 96294e8335a..6e087d13b72 100644
--- a/gfx/layers/d3d9/ImageLayerD3D9.cpp
+++ b/gfx/layers/d3d9/ImageLayerD3D9.cpp
@@ -372,6 +372,11 @@ ImageLayerD3D9::RenderLayer()
   if (image->GetFormat() == Image::CAIRO_SURFACE ||
       image->GetFormat() == Image::REMOTE_IMAGE_BITMAP)
   {
+    NS_ASSERTION(image->GetFormat() != Image::CAIRO_SURFACE ||
+                 !static_cast<CairoImage*>(image)->mSurface ||
+                 static_cast<CairoImage*>(image)->mSurface->GetContentType() != gfxASurface::CONTENT_ALPHA,
+                 "Image layer has alpha image");
+
     bool hasAlpha = false;
     nsRefPtr<IDirect3DTexture9> texture = GetTexture(image, hasAlpha);
 
diff --git a/gfx/layers/opengl/ImageLayerOGL.cpp b/gfx/layers/opengl/ImageLayerOGL.cpp
index 315748649ce..176bc2e2acf 100644
--- a/gfx/layers/opengl/ImageLayerOGL.cpp
+++ b/gfx/layers/opengl/ImageLayerOGL.cpp
@@ -271,6 +271,9 @@ ImageLayerOGL::RenderLayer(int,
       return;
     }
 
+    NS_ASSERTION(cairoImage->mSurface->GetContentType() != gfxASurface::CONTENT_ALPHA,
+                 "Image layer has alpha image");
+
     CairoOGLBackendData *data =
       static_cast<CairoOGLBackendData*>(cairoImage->GetBackendData(LayerManager::LAYERS_OPENGL));
 
@@ -594,6 +597,9 @@ ImageLayerOGL::LoadAsTexture(GLuint aTextureUnit, gfxIntSize* aSize)
     cairoImage->GetBackendData(LayerManager::LAYERS_OPENGL));
 
   if (!data) {
+    NS_ASSERTION(cairoImage->mSurface->GetContentType() == gfxASurface::CONTENT_ALPHA,
+                 "OpenGL mask layers must be backed by alpha surfaces");
+
     // allocate a new texture and save the details in the backend data
     data = new CairoOGLBackendData;
     data->mTextureSize = CalculatePOTSize(cairoImage->mSize, gl());
@@ -775,6 +781,9 @@ ShadowImageLayerOGL::RenderLayer(int aPreviousFrameBuffer,
   mOGLManager->MakeCurrent();
 
   if (mTexImage) {
+    NS_ASSERTION(mTexImage->GetContentType() != gfxASurface::CONTENT_ALPHA,
+                 "Image layer has alpha image");
+
     ShaderProgramOGL *colorProgram =
       mOGLManager->GetProgram(mTexImage->GetShaderProgramType(), GetMaskLayer());
 
@@ -845,6 +854,9 @@ ShadowImageLayerOGL::LoadAsTexture(GLuint aTextureUnit, gfxIntSize* aSize)
 
   mTexImage->BindTextureAndApplyFilter(aTextureUnit);
 
+  NS_ASSERTION(mTexImage->GetContentType() == gfxASurface::CONTENT_ALPHA,
+               "OpenGL mask layers must be backed by alpha surfaces");
+
   // We're assuming that the gl backend won't cheat and use NPOT
   // textures when glContext says it can't (which seems to happen
   // on a mac when you force POT textures)