diff --git a/Function.hpp b/Function.hpp
index d8b52f2..0c9fbee 100644
--- a/Function.hpp
+++ b/Function.hpp
@@ -53,7 +53,7 @@ public:
     }
 
     Function& operator=(std::nullptr_t)     // exploiting that decltype(nullptr) is std::nullptr_t
-    { _is_null = true; }
+    { _is_null = true; return *this; }
 
     Ret operator()(Args... args) const
     {