diff --git a/src/plugins/tls/schannel/CMakeLists.txt b/src/plugins/tls/schannel/CMakeLists.txt
index a7f7fcd99f..57f4927b4f 100644
--- a/src/plugins/tls/schannel/CMakeLists.txt
+++ b/src/plugins/tls/schannel/CMakeLists.txt
@@ -31,4 +31,5 @@ qt_internal_add_plugin(QSchannelBackendPlugin
         ncrypt
     DEFINES
         QT_NO_CAST_FROM_ASCII
+        QT_USE_QSTRINGBUILDER
 )