diff --git a/include/rapidjson/document.h b/include/rapidjson/document.h
index b0f1f70..19f5a6a 100644
--- a/include/rapidjson/document.h
+++ b/include/rapidjson/document.h
@@ -326,6 +326,8 @@ private:
     //! Disallow construction from non-const array
     template<SizeType N>
     GenericStringRef(CharType (&str)[N]) /* = delete */;
+    //! Copy assignment operator not permitted - immutable type
+    GenericStringRef& operator=(const GenericStringRef& rhs) /* = delete */;
 };
 
 //! Mark a character pointer as constant string