diff --git a/servicex/servicex_adapter.py b/servicex/servicex_adapter.py
index baa7b5b0..6c85e85a 100644
--- a/servicex/servicex_adapter.py
+++ b/servicex/servicex_adapter.py
@@ -85,11 +85,21 @@ def _get_bearer_token_file():
                 bearer_token = f.read().strip()
         return bearer_token
 
+    @staticmethod
+    def _effective_expiration(tok) -> float:
+        import sys
+
+        decoded_tok = jwt.decode(tok, verify=False)
+        if "exp" not in decoded_tok:
+            # Token is missing an expiration. Return the maximum float
+            return sys.float_info.max
+        return float(decoded_tok["exp"])
+
     async def _get_authorization(self, force_reauth: bool = False) -> Dict[str, str]:
         now = time.time()
         if (
             self.token
-            and jwt.decode(self.token, verify=False)["exp"] - now > 60
+            and self._effective_expiration(self.token) - now > 60
             and not force_reauth
         ):
             # if less than one minute validity, renew
@@ -105,7 +115,7 @@ async def _get_authorization(self, force_reauth: bool = False) -> Dict[str, str]
             if (
                 not self.token
                 or force_reauth
-                or float(jwt.decode(self.token, verify=False)["exp"]) - now < 60
+                or self._effective_expiration(self.token) - now < 60
             ):
                 await self._get_token()
             return {"Authorization": f"Bearer {self.token}"}
diff --git a/tests/test_servicex_adapter.py b/tests/test_servicex_adapter.py
index 99d8f5c0..2c329caf 100644
--- a/tests/test_servicex_adapter.py
+++ b/tests/test_servicex_adapter.py
@@ -106,16 +106,15 @@ async def test_get_transforms_wlcg_bearer_token(
     )
     token_file.close()
 
-    os.environ["BEARER_TOKEN_FILE"] = token_file.name
+    with patch.dict(os.environ, {"BEARER_TOKEN_FILE": token_file.name}, clear=True):
 
-    # Try with an expired token
-    with pytest.raises(AuthorizationError) as err:
-        decode.return_value = {"exp": 0.0}
-        await servicex.get_transforms()
-        assert "ServiceX access token request rejected:" in str(err.value)
+        # Try with an expired token
+        with pytest.raises(AuthorizationError) as err:
+            decode.return_value = {"exp": 0.0}
+            await servicex.get_transforms()
+            assert "ServiceX access token request rejected:" in str(err.value)
 
     os.remove(token_file.name)
-    del os.environ["BEARER_TOKEN_FILE"]
 
 
 @pytest.mark.asyncio