diff --git a/include/hiddenpointer.h b/include/hiddenpointer.h
index cf6bea09..558da53a 100644
--- a/include/hiddenpointer.h
+++ b/include/hiddenpointer.h
@@ -104,7 +104,7 @@ class HiddenPointer
      *  @param  that
      *  @return HiddenPointer
      */
-    HiddenPointer<Type> operator=(const HiddenPointer &that)
+    HiddenPointer<Type> &operator=(const HiddenPointer &that)
     {
         // skip self assignmend
         if (this == &that) return *this;