diff --git a/_test_data/sandbox/clean/child.txt b/_test_data/sandbox/clean/child.txt
index 276890d..050e125 100644
--- a/_test_data/sandbox/clean/child.txt
+++ b/_test_data/sandbox/clean/child.txt
@@ -1,2 +1,3 @@
 clean stack: child branch
 purpose: child PR on top of sandbox-clean-base
+marker: f16f712