diff --git a/CMakeLists.txt b/CMakeLists.txt
index 603ca53fea..96526218e2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -304,7 +304,7 @@ else()
     set(HAVE_GBM FALSE)
 endif()
 
-if(!KWIN_HAVE_EGL)
+if(NOT KWIN_HAVE_EGL)
     set(HAVE_GBM FALSE)
 endif()