Fix bug introduced in 5b61d59827406ccf5fcde9efb9b0e240823d6b40

theano/compile/debugmode.py

@@ -1674,8 +1674,8 @@ class DebugMode(Mode):
         If any of these arguments (except optimizer) is not None, it overrides the class default.
         The linker arguments is not used. It is set their to allow Mode.requiring() and some other fct to work with DebugMode too.
         """
-        if linker is not None and not isinstance(linker,_Linker):
-            raise Exception("DebugMode can use only its own linker! Don't give him one to use it.")
+        if linker is not None and not issubclass(linker, _Linker):
+            raise Exception("DebugMode can use only its own linker! Don't give him one to use it.", linker)
 
         super(DebugMode, self).__init__(
                 optimizer=optimizer,