diff --git a/MyxCMake/backports/TopLevelProject.cmake b/MyxCMake/backports/TopLevelProject.cmake
index 7dbccec..953758f 100644
--- a/MyxCMake/backports/TopLevelProject.cmake
+++ b/MyxCMake/backports/TopLevelProject.cmake
@@ -3,7 +3,9 @@ include_guard(GLOBAL)
 if(${CMAKE_VERSION} VERSION_LESS 3.21)
   get_property(__parent_directory DIRECTORY PROPERTY PARENT_DIRECTORY)
   if(NOT __parent_directory)
-    set(PROJECT_IS_TOP_LEVEL true)
+    set(PROJECT_IS_TOP_LEVEL TRUE)
+  else()
+    set(PROJECT_IS_TOP_LEVEL FALSE)
   endif()
   unset(__parent_directory)
 endif()