diff --git a/src/runtime/methodbinder.cs b/src/runtime/methodbinder.cs
index 22aaf33e4..f2ee104fc 100644
--- a/src/runtime/methodbinder.cs
+++ b/src/runtime/methodbinder.cs
@@ -344,7 +344,7 @@ internal Binding Bind(IntPtr inst, IntPtr args, IntPtr kw,
                             if (clrtype != null)
                             {
                                 bool typematch = false;
-                                if (pi[n].ParameterType != clrtype)
+                                if ((pi[n].ParameterType != clrtype) && !(pi[n].ParameterType.IsAssignableFrom(clrtype)))
                                 {
                                     IntPtr pytype = Converter.GetPythonTypeByAlias(pi[n].ParameterType);
                                     pyoptype = Runtime.PyObject_Type(op);
@@ -603,4 +603,4 @@ internal Binding(MethodBase info, Object inst, Object[] args,
             this.outs = outs;
         }
     }
-}
\ No newline at end of file
+}