diff --git a/tests/bootstrap_test.sh b/tests/bootstrap_test.sh
index 98e3b66..7265ac5 100755
--- a/tests/bootstrap_test.sh
+++ b/tests/bootstrap_test.sh
@@ -126,7 +126,7 @@
 
   # This test needs to start from a clean build, but setup creates an
   # initialized tree that has already been built once.  Clear the out
-  # directory to start from scratch.
+  # directory to start from scratch (see b/185591972)
   rm -rf out
 
   mkdir -p a