diff --git a/string/test/conv_test.cpp b/string/test/conv_test.cpp
index 82f8d8f..ca3c5ff 100644
--- a/string/test/conv_test.cpp
+++ b/string/test/conv_test.cpp
@@ -82,8 +82,8 @@ void conv_test()
     to_upper( str3 );
     BOOST_CHECK( str3=="" );
 
-    free(pch1);
-    free(pch2);
+    delete[] pch1;
+    delete[] pch2;
 }
 
 // test main