diff --git a/lib/server.js b/lib/server.js
index 07e5338..fbb0dc7 100644
--- a/lib/server.js
+++ b/lib/server.js
@@ -2428,6 +2428,9 @@ WalletService.prototype.getFiatRate = function(opts, cb) {
 };
 
 WalletService.prototype.pushNotificationsSubscribe = function(opts, cb) {
+  if (!Utils.checkRequired(opts, ['token']))
+    return cb(new ClientError('Required argument missing'));
+
   var self = this;
 
   opts.user = self.walletId + '$' + self.copayerId + '$' + opts.token;