diff --git a/.arcconfig b/.arcconfig
index 783f1d2..e0467e9 100644
--- a/.arcconfig
+++ b/.arcconfig
@@ -1,3 +1,4 @@
 {
-  "phabricator.uri": "https://secure.phabricator.com/"
+  "phabricator.uri": "https://secure.phabricator.com/",
+  "history.immutable": false
 }