diff --git a/src/corelib/CMakeLists.txt b/src/corelib/CMakeLists.txt
index 4fa158639e4..6b6836df811 100644
--- a/src/corelib/CMakeLists.txt
+++ b/src/corelib/CMakeLists.txt
@@ -336,6 +336,7 @@ 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