diff --git a/src/corelib/serialization/qcborcommon.h b/src/corelib/serialization/qcborcommon.h
index 1e33a5bae48..2ea0cec44c5 100644
--- a/src/corelib/serialization/qcborcommon.h
+++ b/src/corelib/serialization/qcborcommon.h
@@ -50,7 +50,6 @@
 
 /* X11 headers use these values too, but as defines */
 #if defined(False) && defined(True)
-#  define QT_X11_DEFINES_FOUND 1
 #  undef True
 #  undef False
 #endif
diff --git a/src/corelib/serialization/qcborstreamreader.h b/src/corelib/serialization/qcborstreamreader.h
index 6d5feccfcf2..3665b09ea8c 100644
--- a/src/corelib/serialization/qcborstreamreader.h
+++ b/src/corelib/serialization/qcborstreamreader.h
@@ -49,8 +49,8 @@
 
 QT_REQUIRE_CONFIG(cborstreamreader);
 
-// See qcborcommon.h for why we check
-#if defined(QT_X11_DEFINES_FOUND)
+/* X11 headers use these values too, but as defines */
+#if defined(False) && defined(True)
 #  undef True
 #  undef False
 #endif
diff --git a/src/corelib/serialization/qcborstreamwriter.h b/src/corelib/serialization/qcborstreamwriter.h
index f8c94ceb938..9c2f9e81ab0 100644
--- a/src/corelib/serialization/qcborstreamwriter.h
+++ b/src/corelib/serialization/qcborstreamwriter.h
@@ -51,8 +51,8 @@
 
 QT_REQUIRE_CONFIG(cborstreamwriter);
 
-// See qcborcommon.h for why we check
-#if defined(QT_X11_DEFINES_FOUND)
+/* X11 headers use these values too, but as defines */
+#if defined(False) && defined(True)
 #  undef True
 #  undef False
 #endif
diff --git a/src/corelib/serialization/qcborvalue.h b/src/corelib/serialization/qcborvalue.h
index fd9f78a88d7..9a26c9ab66e 100644
--- a/src/corelib/serialization/qcborvalue.h
+++ b/src/corelib/serialization/qcborvalue.h
@@ -52,8 +52,8 @@
 #include <QtCore/quuid.h>
 #include <QtCore/qvariant.h>
 
-// See qcborcommon.h for why we check
-#if defined(QT_X11_DEFINES_FOUND)
+/* X11 headers use these values too, but as defines */
+#if defined(False) && defined(True)
 #  undef True
 #  undef False
 #endif