--- a/services/sync/modules/record.js
+++ b/services/sync/modules/record.js
@@ -406,16 +406,24 @@ CollectionKeyManager.prototype = {
   generateNewKeysWBO: function(collections) {
     let newDefaultKey, newColls;
     [newDefaultKey, newColls] = this.newKeys(collections);
 
     return this._makeWBO(newColls, newDefaultKey);
   },
 
   /**
+   * Generate a new default key, since without one you cannot use setContents.
+   */
+  generateDefaultKey: function() {
+    this._default = new BulkKeyBundle(DEFAULT_KEYBUNDLE_NAME);
+    this._default.generateRandom();
+  },
+
+  /**
    * Return true if keys are already present for each of the given
    * collections.
    */
   hasKeysFor: function(collections) {
     // We can't use filter() here because sometimes collections is an iterator.
     for (let collection of collections) {
       if (!this._collections[collection]) return false;
     }