diff --git a/include/common.h b/include/common.h
index 0923735..88322ca 100644
--- a/include/common.h
+++ b/include/common.h
@@ -108,7 +108,7 @@ class OBTypeM<Func,O1,O...>: public OBTypeM<Func,O...>
   return true;
  }
  template<class... Args>
- auto operator ()(Args... args) -> decltype(Func<O1>()(dynamic_cast<const O1*>(this->P()),args...)) const
+ auto operator ()(Args... args) const -> decltype(Func<O1>()(dynamic_cast<const O1*>(this->P()),args...))
  {
   typedef decltype(Func<O1>()(dynamic_cast<const O1*>(this->P()),args...)) T;
   if(right) return Func<O1>()(dynamic_cast<const O1*>(OBTypeM<Func,O...>::P()),args...);