diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index 30ff865341..1b771e67a6 100644
--- a/src/corelib/CMakeLists.txt
+++ b/src/corelib/CMakeLists.txt
@@ -332,6 +332,7 @@ qt_internal_add_module(Core
     NO_PCH_SOURCES
         compat/removed_api.cpp
         global/qsimd.cpp
+        kernel/qsocketnotifier.cpp # defines BUILDING_QSOCKETNOTIFIER
     DEFINES
         QT_NO_CONTEXTLESS_CONNECT
         QT_NO_FOREACH