diff --git a/src/agents/extensions/sandbox/vercel/sandbox.py b/src/agents/extensions/sandbox/vercel/sandbox.py
index 92513077ab..c87438cb73 100644
--- a/src/agents/extensions/sandbox/vercel/sandbox.py
+++ b/src/agents/extensions/sandbox/vercel/sandbox.py
@@ -460,18 +460,17 @@ async def _resolve_exposed_port(self, port: int) -> ExposedPortEndpoint:
 
         parsed = urlsplit(domain)
         host = parsed.hostname
-        if not host:
+        if not host or parsed.scheme != "https":
             raise ExposedPortUnavailableError(
                 port=port,
                 exposed_ports=self.state.exposed_ports,
                 reason="backend_unavailable",
                 context={"backend": "vercel", "domain": domain},
             )
-        tls = parsed.scheme == "https"
         return ExposedPortEndpoint(
             host=host,
-            port=parsed.port or (443 if tls else 80),
-            tls=tls,
+            port=parsed.port or 443,
+            tls=True,
         )
 
     async def read(self, path: Path, *, user: str | User | None = None) -> io.IOBase:
diff --git a/tests/extensions/sandbox/test_vercel.py b/tests/extensions/sandbox/test_vercel.py
index 306acf9527..1941ba1ed3 100644
--- a/tests/extensions/sandbox/test_vercel.py
+++ b/tests/extensions/sandbox/test_vercel.py
@@ -16,7 +16,11 @@
 from agents.sandbox import Manifest, SandboxPathGrant
 from agents.sandbox.entries import File, InContainerMountStrategy, Mount, MountpointMountPattern
 from agents.sandbox.entries.mounts.base import InContainerMountAdapter
-from agents.sandbox.errors import ConfigurationError, InvalidManifestPathError
+from agents.sandbox.errors import (
+    ConfigurationError,
+    ExposedPortUnavailableError,
+    InvalidManifestPathError,
+)
 from agents.sandbox.manifest import Environment
 from agents.sandbox.materialization import MaterializedFile
 from agents.sandbox.session.base_sandbox_session import BaseSandboxSession
@@ -541,6 +545,29 @@ async def test_vercel_exec_read_write_and_port_resolution(monkeypatch: pytest.Mo
     assert payload.read() == b"payload"
 
 
+@pytest.mark.asyncio
+async def test_vercel_resolve_exposed_port_rejects_non_https_domain(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    vercel_module = _load_vercel_module(monkeypatch)
+
+    state = vercel_module.VercelSandboxSessionState(
+        session_id="00000000-0000-0000-0000-000000000099",
+        manifest=Manifest(),
+        snapshot=NoopSnapshot(id="snapshot"),
+        sandbox_id="sandbox-http",
+        exposed_ports=(3000,),
+    )
+    sandbox = _FakeAsyncSandbox(
+        sandbox_id="sandbox-http",
+        routes=[{"port": 3000, "url": "http://3000-sandbox.vercel.run"}],
+    )
+    session = vercel_module.VercelSandboxSession.from_state(state, sandbox=sandbox)
+
+    with pytest.raises(ExposedPortUnavailableError):
+        await session.resolve_exposed_port(3000)
+
+
 @pytest.mark.asyncio
 async def test_vercel_start_uses_base_session_contract_and_materializes_workspace(
     monkeypatch: pytest.MonkeyPatch,