diff --git a/README.md b/README.md
index 1601d3b5..13eeafbb 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,7 @@ The Alpaca SDK will check the environment for a number of variables which can be
 | APCA_RETRY_WAIT=3 | 3 | seconds to wait between each retry attempt |
 | APCA_RETRY_CODES=429,504 | 429,504 | comma-separated HTTP status code for which retry is attempted |
 | POLYGON_WS_URL | wss://alpaca.socket.polygon.io/stocks | Endpoint for streaming polygon data.  You likely don't need to change this unless you want to proxy it for example |
+| POLYGON_KEY_ID | | Your Polygon key, if it's not the same as your Alpaca API key. Most users will not need to set this to access Polygon.|
 
 
 ## REST
@@ -238,9 +239,10 @@ Deregisters the event handler function that was previously registered via `on` o
 ---
 # Polygon API Service
 
-Alpaca's API key ID can be used to access Polygon API whose document is found [here](https://polygon.io/docs/).
-This python SDK wraps their API service and seamlessly integrates with Alpaca API.
-`alpaca_trade_api.REST.polygon` will be the `REST` object for Polygon.
+Alpaca's API key ID can be used to access Polygon API, the documentation for
+which is found [here](https://polygon.io/docs/).
+This python SDK wraps their API service and seamlessly integrates it with the Alpaca
+API. `alpaca_trade_api.REST.polygon` will be the `REST` object for Polygon.
 
 The example below gives AAPL daily OHLCV data in a DataFrame format.
 
diff --git a/alpaca_trade_api/common.py b/alpaca_trade_api/common.py
index 6b5b8200..e5b3ca2c 100644
--- a/alpaca_trade_api/common.py
+++ b/alpaca_trade_api/common.py
@@ -23,6 +23,17 @@ def get_credentials(key_id=None, secret_key=None):
     return key_id, secret_key
 
 
+def get_polygon_credentials(alpaca_key=None):
+    try:
+        alpaca_key, _ = get_credentials(alpaca_key)
+    except ValueError:
+        pass
+    key_id = os.environ.get('POLYGON_KEY_ID') or alpaca_key
+    if key_id is None:
+        raise ValueError('Key ID must be given to access Polygon API')
+    return key_id
+
+
 def get_api_version(api_version):
     api_version = api_version or os.environ.get('APCA_API_VERSION')
     if api_version is None:
diff --git a/alpaca_trade_api/polygon/rest.py b/alpaca_trade_api/polygon/rest.py
index 73576f84..46606e8f 100644
--- a/alpaca_trade_api/polygon/rest.py
+++ b/alpaca_trade_api/polygon/rest.py
@@ -6,6 +6,7 @@
     Exchange, SymbolTypeMap, ConditionMap,
     Company, Dividends, Splits, Earnings, Financials, NewsList, Ticker
 )
+from alpaca_trade_api.common import get_polygon_credentials
 
 
 def _is_list_like(o):
@@ -15,6 +16,7 @@ def _is_list_like(o):
 class REST(object):
 
     def __init__(self, api_key, staging=False):
+        self._api_key = get_polygon_credentials(api_key)
         self._api_key = api_key
         self._staging = staging
         self._session = requests.Session()
diff --git a/alpaca_trade_api/polygon/stream2.py b/alpaca_trade_api/polygon/stream2.py
index c68f058f..2bbca98b 100644
--- a/alpaca_trade_api/polygon/stream2.py
+++ b/alpaca_trade_api/polygon/stream2.py
@@ -7,12 +7,13 @@
 from .entity import (
     Quote, Trade, Agg, Entity,
 )
+from alpaca_trade_api.common import get_polygon_credentials
 import logging
 
 
 class StreamConn(object):
     def __init__(self, key_id=None):
-        self._key_id = key_id or os.environ.get('APCA_API_KEY_ID')
+        self._key_id = get_polygon_credentials(key_id)
         self._endpoint = os.environ.get(
             'POLYGON_WS_URL',
             'wss://alpaca.socket.polygon.io/stocks'