diff --git a/lib/modifiedCanvasAPI.js b/lib/modifiedCanvasAPI.js
index 42797af..3dac897 100644
--- a/lib/modifiedCanvasAPI.js
+++ b/lib/modifiedCanvasAPI.js
@@ -359,6 +359,11 @@
 			object: "HTMLCanvasElement",
 			fakeGenerator: function(checker){
 				return function toBlob(callback){
+					if (this instanceof toBlob){
+						throw new extension.getWrapped(window).TypeError(
+							"HTMLCanvasElement.prototype.toBlob is not a constructor"
+						);
+					}
 					return checkerWrapper(checker, this, arguments, useFakeCanvasCallback);
 				};
 			},