diff --git a/.changelog/tall-pigs-sing.md b/.changelog/tall-pigs-sing.md
new file mode 100644
index 0000000..1e2432f
--- /dev/null
+++ b/.changelog/tall-pigs-sing.md
@@ -0,0 +1,5 @@
+---
+pympp: patch
+---
+
+Fixed fail-closed expiry enforcement in `ChargeIntent.verify`: requests with a missing `expires` challenge parameter are now rejected instead of silently allowed through.
diff --git a/src/mpp/methods/tempo/client.py b/src/mpp/methods/tempo/client.py
index 2562baa..4f14cbc 100644
--- a/src/mpp/methods/tempo/client.py
+++ b/src/mpp/methods/tempo/client.py
@@ -217,9 +217,7 @@ async def _build_tempo_transfer(
         # (smart wallet), not the access key address.
         nonce_address = self.root_account if self.root_account else self.account.address
 
-        chain_id, on_chain_nonce, gas_price = await get_tx_params(
-            resolved_rpc, nonce_address
-        )
+        chain_id, on_chain_nonce, gas_price = await get_tx_params(resolved_rpc, nonce_address)
 
         if expected_chain_id is not None and chain_id != expected_chain_id:
             raise TransactionError(
@@ -238,9 +236,7 @@ async def _build_tempo_transfer(
 
         gas_limit = DEFAULT_GAS_LIMIT
         try:
-            estimated = await estimate_gas(
-                resolved_rpc, nonce_address, currency, transfer_data
-            )
+            estimated = await estimate_gas(resolved_rpc, nonce_address, currency, transfer_data)
             gas_limit = max(gas_limit, estimated + 5_000)
         except Exception:
             pass
diff --git a/src/mpp/methods/tempo/intents.py b/src/mpp/methods/tempo/intents.py
index 8d582ab..57cb111 100644
--- a/src/mpp/methods/tempo/intents.py
+++ b/src/mpp/methods/tempo/intents.py
@@ -209,12 +209,13 @@ async def verify(
         req = ChargeRequest.model_validate(request)
 
         # Expiry is conveyed via the challenge-level expires auth-param,
-        # not inside the request body.
+        # not inside the request body.  Fail closed: reject if missing.
         challenge_expires = credential.challenge.expires
-        if challenge_expires:
-            expires = datetime.fromisoformat(challenge_expires.replace("Z", "+00:00"))
-            if expires < datetime.now(UTC):
-                raise VerificationError("Request has expired")
+        if not challenge_expires:
+            raise VerificationError("Request has expired (no expires)")
+        expires = datetime.fromisoformat(challenge_expires.replace("Z", "+00:00"))
+        if expires < datetime.now(UTC):
+            raise VerificationError("Request has expired")
 
         payload_data = credential.payload
         if not isinstance(payload_data, dict) or "type" not in payload_data:
diff --git a/tests/test_tempo.py b/tests/test_tempo.py
index 479c602..492c9b9 100644
--- a/tests/test_tempo.py
+++ b/tests/test_tempo.py
@@ -194,6 +194,22 @@ async def test_verify_expired_request(self) -> None:
                 },
             )
 
+    @pytest.mark.asyncio
+    async def test_verify_missing_expires_rejected(self) -> None:
+        """Should reject credentials with no expires (fail-closed)."""
+        intent = ChargeIntent(rpc_url="https://rpc.test")
+        credential = make_credential(payload={"type": "hash", "hash": "0x123"}, expires=None)
+
+        with pytest.raises(VerificationError, match="no expires"):
+            await intent.verify(
+                credential,
+                {
+                    "amount": "1000",
+                    "currency": "0x123",
+                    "recipient": "0x456",
+                },
+            )
+
     @pytest.mark.asyncio
     async def test_verify_invalid_payload(self) -> None:
         """Should reject invalid credential payload."""
@@ -1423,6 +1439,7 @@ async def test_access_key_builds_keychain_signature(self, httpx_mock: HTTPXMock)
 
         assert credential.payload["type"] == "transaction"
         # source should be the root account, not the access key
+        assert credential.source is not None
         assert root.lower() in credential.source.lower()
         assert access_key.address.lower() not in credential.source.lower()
 
@@ -1462,6 +1479,7 @@ async def test_access_key_with_fee_payer(self, httpx_mock: HTTPXMock) -> None:
 
         assert credential.payload["type"] == "transaction"
         assert credential.payload["signature"].startswith("0x78")
+        assert credential.source is not None
         assert root.lower() in credential.source.lower()
 
     @pytest.mark.asyncio
@@ -1496,6 +1514,7 @@ async def test_no_root_account_uses_regular_signing(self, httpx_mock: HTTPXMock)
         credential = await method.create_credential(challenge)
 
         assert credential.payload["type"] == "transaction"
+        assert credential.source is not None
         assert account.address in credential.source