diff --git a/src/crypto/algorithms/base.js b/src/crypto/algorithms/base.js
index 5d9df319d..ad19f6fd0 100644
--- a/src/crypto/algorithms/base.js
+++ b/src/crypto/algorithms/base.js
@@ -163,6 +163,8 @@ utils.inherits(module.exports.DecryptionError, Error);
  *
  * @constructor
  * @param {string} msg message describing the problem
+ * @param {Object} devices userId -> {deviceId -> object}
+ *      set of unknown devices per user we're warning about
  * @extends Error
  */
 module.exports.UnknownDeviceError = function(msg, devices) {
diff --git a/src/crypto/algorithms/megolm.js b/src/crypto/algorithms/megolm.js
index 54c2660fd..8803d31d1 100644
--- a/src/crypto/algorithms/megolm.js
+++ b/src/crypto/algorithms/megolm.js
@@ -423,12 +423,15 @@ MegolmEncryption.prototype.encryptMessage = function(room, eventType, content) {
  * Checks the devices we're about to send to and see if any are entirely
  * unknown to the user.  If so, warn the user, and mark them as known to
  * give the user a chance to go verify them before re-sending this message.
+ *
+ * @param {Object} devicesInRoom userId -> {deviceId -> object}
+ *   devices we should shared the session with.
  */
 MegolmEncryption.prototype._checkForUnknownDevices = function(devicesInRoom) {
     const unknownDevices = {};
 
-    Object.keys(devicesInRoom).forEach(userId=>{
-        Object.keys(devicesInRoom[userId]).forEach(deviceId=>{
+    Object.keys(devicesInRoom).forEach((userId)=>{
+        Object.keys(devicesInRoom[userId]).forEach((deviceId)=>{
             const device = devicesInRoom[userId][deviceId];
             if (device.isUnverified() && !device.isKnown()) {
                 // mark the devices as known to the user, given we're about to