diff --git a/library/include/DataDefs.h b/library/include/DataDefs.h
index 0109f0fd0..e03e9a0a8 100644
--- a/library/include/DataDefs.h
+++ b/library/include/DataDefs.h
@@ -499,23 +499,27 @@ namespace df
 
     template<class T>
     typename std::enable_if<
-        std::is_copy_assignable<T>::value
+        std::is_copy_assignable<T>::value,
+        void*
     >::type allocator_try_assign(void *out, const void *in) {
         *(T*)out = *(const T*)in;
+        return out;
     }
 
     template<class T>
     typename std::enable_if<
-        !std::is_copy_assignable<T>::value
+        !std::is_copy_assignable<T>::value,
+        void*
     >::type allocator_try_assign(void *out, const void *in) {
         // assignment is not possible; do nothing
+        return NULL;
     }
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wdelete-non-virtual-dtor"
     template<class T>
     void *allocator_fn(void *out, const void *in) {
-        if (out) { allocator_try_assign<T>(out, in); return out; }
+        if (out) { return allocator_try_assign<T>(out, in); }
         else if (in) { delete (T*)in; return (T*)in; }
         else return new T();
     }