diff --git a/testsuite/css/meson.build b/testsuite/css/meson.build
index f8d13fe548..cd35ced891 100644
--- a/testsuite/css/meson.build
+++ b/testsuite/css/meson.build
@@ -6,6 +6,7 @@ csstest_env.set('G_TEST_BUILDDIR', meson.current_build_dir())
 csstest_env.set('GIO_USE_VFS', 'local')
 csstest_env.set('GSETTINGS_BACKEND', 'memory')
 csstest_env.set('G_ENABLE_DIAGNOSTIC', '0')
+csstest_env.set('GDK_DEBUG', 'default-settings')
 
 subdir('parser')
 subdir('nodes')