diff --git a/src/dstack/api/_public/runs.py b/src/dstack/api/_public/runs.py
index af54924fb..6097b689d 100644
--- a/src/dstack/api/_public/runs.py
+++ b/src/dstack/api/_public/runs.py
@@ -326,8 +326,9 @@ def attach(
 
             # TODO: get login name from runner in case it's not specified in the run configuration
             # (i.e. the default image user is used, and it is not root)
-            container_user = self._run.run_spec.configuration.user
-            if container_user is None:
+            if job.job_spec.user is not None and job.job_spec.user.username is not None:
+                container_user = job.job_spec.user.username
+            else:
                 container_user = "root"
 
             self._ssh_attach = SSHAttach(