diff --git a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
@@ -127,9 +127,9 @@
     // This is suppressing "added <address> to the list of known hosts"
     // messages, which are confusing and irrelevant when they arise from
     // proxied requests. It might also be suppressing lots of useful errors,
-    // of course. Ideally, we would enforce host keys eventually.
+    // of course. Ideally, we would enforce host keys eventually. See T13121.
     $options[] = '-o';
-    $options[] = 'LogLevel=quiet';
+    $options[] = 'LogLevel=ERROR';
 
     // NOTE: We prefix the command with "@username", which the far end of the
     // connection will parse in order to act as the specified user. This
diff --git a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
--- a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
+++ b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
@@ -30,8 +30,11 @@
     $full_command = call_user_func_array('csprintf', $argv);
 
     $flags = array();
+
+    // See T13121. Attempt to suppress the "Permanently added X to list of
+    // known hosts" message without suppressing anything important.
     $flags[] = '-o';
-    $flags[] = 'LogLevel=quiet';
+    $flags[] = 'LogLevel=ERROR';
 
     $flags[] = '-o';
     $flags[] = 'StrictHostKeyChecking=no';