diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 3d2b45d21..11f76c06f 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -372,7 +372,8 @@ class Auth(object):
             defer.returnValue((user, ClientInfo(device_id, token_id)))
         except KeyError:
             raise AuthError(
-                self.TOKEN_NOT_FOUND_HTTP_STATUS, "Missing access token."
+                self.TOKEN_NOT_FOUND_HTTP_STATUS, "Missing access token.",
+                errcode=Codes.MISSING_TOKEN
             )
 
     @defer.inlineCallbacks
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index eddd88977..109547b3c 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -31,6 +31,7 @@ class Codes(object):
     BAD_PAGINATION = "M_BAD_PAGINATION"
     UNKNOWN = "M_UNKNOWN"
     NOT_FOUND = "M_NOT_FOUND"
+    MISSING_TOKEN = "M_MISSING_TOKEN"
     UNKNOWN_TOKEN = "M_UNKNOWN_TOKEN"
     LIMIT_EXCEEDED = "M_LIMIT_EXCEEDED"
     CAPTCHA_NEEDED = "M_CAPTCHA_NEEDED"