diff --git a/.cmake.conf b/.cmake.conf
index ee63c78947d..9d09fbd7c8d 100644
--- a/.cmake.conf
+++ b/.cmake.conf
@@ -1,3 +1,12 @@
+# set (git) module specific defines, but only if we are actually qtbase
+# do _not_ set them as the global toplevel configuration
+# we check for QT_REPO_MODULE_VERSION before defining it below; that will
+# ensure that when this file is included the second time in a toplevel buld
+# (directly by qtbase) we actually add the extra definitions
+if (NOT DEFINED QT_SUPERBUILD OR DEFINED QT_REPO_MODULE_VERSION)
+    set(QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_LEAN_HEADERS=1")
+endif()
+
 set(QT_REPO_MODULE_VERSION "6.4.0")
 set(QT_REPO_MODULE_PRERELEASE_VERSION_SEGMENT "alpha1")
 
@@ -22,6 +31,3 @@ set(QT_SUPPORTED_MIN_CMAKE_VERSION_FOR_USING_QT_STATIC "3.21")
 #       in sync.
 set(QT_MIN_NEW_POLICY_CMAKE_VERSION "3.16")
 set(QT_MAX_NEW_POLICY_CMAKE_VERSION "3.21")
-
-# set (git) module specific defines
-set(QT_EXTRA_INTERNAL_TARGET_DEFINES "QT_LEAN_HEADERS=1")