diff --git a/src/components/structures/RoomSubList.js b/src/components/structures/RoomSubList.js
index e1b2f96eb5..251c65226c 100644
--- a/src/components/structures/RoomSubList.js
+++ b/src/components/structures/RoomSubList.js
@@ -327,43 +327,46 @@ var RoomSubList = React.createClass({
     },
 
     calcManualOrderTagData: function(room) {
-        var index = this.state.sortedList.indexOf(room);
+        const index = this.state.sortedList.indexOf(room);
 
         // we sort rooms by the lexicographic ordering of the 'order' metadata on their tags.
         // for convenience, we calculate this for now a floating point number between 0.0 and 1.0.
 
-        var orderA = 0.0; // by default we're next to the beginning of the list
+        let orderA = 0.0; // by default we're next to the beginning of the list
         if (index > 0) {
-            var prevTag = this.state.sortedList[index - 1].tags[this.props.tagName];
+            const prevTag = this.state.sortedList[index - 1].tags[this.props.tagName];
             if (!prevTag) {
-                console.error("Previous room in sublist is not tagged to be in this list. This should never happen.")
-            }
-            else if (prevTag.order === undefined) {
+                console.error("Previous room in sublist is not tagged to be in this list. This should never happen.");
+            } else if (prevTag.order === undefined) {
                 console.error("Previous room in sublist has no ordering metadata. This should never happen.");
-            }
-            else {
+            } else {
                 orderA = prevTag.order;
             }
         }
 
-        var orderB = 1.0; // by default we're next to the end of the list too
+        let orderB = 1.0; // by default we're next to the end of the list too
         if (index < this.state.sortedList.length - 1) {
-            var nextTag = this.state.sortedList[index + 1].tags[this.props.tagName];
+            const nextTag = this.state.sortedList[index + 1].tags[this.props.tagName];
             if (!nextTag) {
-                console.error("Next room in sublist is not tagged to be in this list. This should never happen.")
-            }
-            else if (nextTag.order === undefined) {
+                console.error("Next room in sublist is not tagged to be in this list. This should never happen.");
+            } else if (nextTag.order === undefined) {
                 console.error("Next room in sublist has no ordering metadata. This should never happen.");
-            }
-            else {
+            } else {
                 orderB = nextTag.order;
             }
         }
 
-        var order = (orderA + orderB) / 2.0;
+        const order = (orderA + orderB) / 2.0;
+
         if (order === orderA || order === orderB) {
             console.error("Cannot describe new list position.  This should be incredibly unlikely.");
-            // TODO: renumber the list
+            this.state.sortedList.forEach((room, index) => {
+                MatrixClientPeg.get().setRoomTag(
+                    room.roomId, this.props.tagName,
+                    {order: index / this.state.sortedList.length},
+                );
+            });
+            return index / this.state.sortedList.length;
         }
 
         return order;