diff --git a/docsgpt/deploy/commands.py b/docsgpt/deploy/commands.py
index 8b1503a6..0811134f 100644
--- a/docsgpt/deploy/commands.py
+++ b/docsgpt/deploy/commands.py
@@ -862,7 +862,9 @@ def doctor(args, context: Optional[Context] = None) -> int:
         _check_provider(env),
     ]
 
-    port = int(env.get("DOCSGPT_PORT") or stack.DEFAULT_PORT)
+    # The one command that exists to explain a broken setup must not fall over on one.
+    port = _port_number(env["DOCSGPT_PORT"], f"DOCSGPT_PORT in {env_path}") if env.get("DOCSGPT_PORT") \
+        else stack.DEFAULT_PORT
     if _port_is_free(port):
         checks.append(Check("port", "ok", f"{port} is free"))
     else:
diff --git a/tests/deploy/test_doctor.py b/tests/deploy/test_doctor.py
index b92104ce..3cc94dfd 100644
--- a/tests/deploy/test_doctor.py
+++ b/tests/deploy/test_doctor.py
@@ -274,6 +274,17 @@ class TestDoctor:
         assert "FAIL" in captured.out
         assert "1 problem" in captured.err
 
+    def test_a_hand_edited_port_is_reported_not_raised(self, tmp_path, monkeypatch):
+        """Doctor exists to explain a broken setup, so it must not traceback on one."""
+        self._only(
+            monkeypatch,
+            commands.Check("postgres", "ok", "fine"),
+            commands.Check("redis", "ok", "fine"),
+        )
+        (tmp_path / ".env").write_text("DOCSGPT_PORT=seven thousand\n", encoding="utf-8")
+        with pytest.raises(DeployError, match="not a port number"):
+            _run(["doctor", "--dir", str(tmp_path)], _context())
+
     def test_it_says_which_settings_file_it_read(self, tmp_path, capsys, monkeypatch):
         self._only(
             monkeypatch,