diff --git a/cmake/QtBuild.cmake b/cmake/QtBuild.cmake
index 11a4b66e3f..9e7db08f9b 100644
--- a/cmake/QtBuild.cmake
+++ b/cmake/QtBuild.cmake
@@ -675,7 +675,7 @@ function(qt_ensure_sync_qt)
 
     # When building qtbase, use the source syncqt, otherwise use the installed one.
     set(SYNCQT_FROM_SOURCE "${QtBase_SOURCE_DIR}/bin/syncqt.pl")
-    if(EXISTS "${SYNCQT_FROM_SOURCE}")
+    if(NOT ("${QtBase_SOURCE_DIR}" STREQUAL "") AND EXISTS "${SYNCQT_FROM_SOURCE}")
         set(QT_SYNCQT "${SYNCQT_FROM_SOURCE}" CACHE FILEPATH "syncqt script")
         message(STATUS "Using source syncqt found at: ${QT_SYNCQT}")