diff --git a/content/canvas/src/WebGLContext.cpp b/content/canvas/src/WebGLContext.cpp
index 5a444fcbb171..5b5e9a104460 100644
--- a/content/canvas/src/WebGLContext.cpp
+++ b/content/canvas/src/WebGLContext.cpp
@@ -500,6 +500,11 @@ WebGLContext::SetDimensions(PRInt32 width, PRInt32 height)
             }
         }
     }
+
+    if (gl && gl->IsANGLE() && !gl->GetD3DShareHandle()) {
+        NS_NOTREACHED("ANGLE should always provide d3d share handles!");
+        gl = nsnull;
+    }
 #endif
 
     // try the default provider, whatever that is