diff --git a/scripts/ssh/ssh-connect.php b/scripts/ssh/ssh-connect.php
--- a/scripts/ssh/ssh-connect.php
+++ b/scripts/ssh/ssh-connect.php
@@ -53,6 +53,12 @@
 $pattern[] = '-o';
 $pattern[] = 'UserKnownHostsFile=/dev/null';
 
+// This suppresses the "Permanently added ... to the list of known hosts"
+// message, which is always output because we set `UserKnownHostsFile` to
+// `/dev/null`.
+$pattern[] = '-o';
+$pattern[] = 'LogLevel=ERROR';
+
 $as_device = getenv('PHABRICATOR_AS_DEVICE');
 $credential_phid = getenv('PHABRICATOR_CREDENTIAL');