diff --git a/src/jsonexpression.h b/src/jsonexpression.h
index 2d149f5..6397407 100644
--- a/src/jsonexpression.h
+++ b/src/jsonexpression.h
@@ -5,7 +5,7 @@
  */
 
 /*
- * Copyright (c) 2018, Tomasz Sowa
+ * Copyright (c) 2018-2021, Tomasz Sowa
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -67,6 +67,9 @@ protected:
 	void before_field_value_list();
 	void after_field_value_list();
 
+	// using FlatExpression::esc to suppress clang warning:
+	// 'morm::JSONExpression::esc' hides overloaded virtual function [-Woverloaded-virtual]
+	using FlatExpression::esc;
 
 	void esc(char val, PT::TextStream & stream);