diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5af88738308..59150bc1d12 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -425,6 +425,7 @@ if(WITH_CORE)
   else()
     set(QT_MIN_VERSION 5.12.0)
     set(QT_VERSION_BASE "Qt5")
+    set(WITH_QT5_KDE_FORK FALSE CACHE BOOL "Using KDE's Qt 5.15 fork")
   endif()
 
   # Use Qt5SerialPort optionally for GPS
diff --git a/cmake_templates/qgsconfig.h.in b/cmake_templates/qgsconfig.h.in
index 479134c2887..eae29b00b09 100644
--- a/cmake_templates/qgsconfig.h.in
+++ b/cmake_templates/qgsconfig.h.in
@@ -104,5 +104,7 @@
 
 #cmakedefine ENABLE_TESTS
 
+#cmakedefine WITH_QT5_KDE_FORK
+
 #endif