diff --git a/js/id/actions/merge_polygon.js b/js/id/actions/merge_polygon.js
index 8eb94766f..7472837ae 100644
--- a/js/id/actions/merge_polygon.js
+++ b/js/id/actions/merge_polygon.js
@@ -20,14 +20,27 @@ iD.actions.MergePolygon = function(ids) {
     var action = function(graph) {
         var entities = groupEntities(graph);
 
-        // an array of all the polygons to be merged
-        var polygons = _.unique(entities.multipolygon.reduce(function(polygons, m) {
-            return polygons.concat(m.members.filter(function(d) {
-                return d.type === 'way';
-            }).map(function(d) {
-                return graph.entity(d.id);
-            }));
-        }, entities.closedWay));
+        // An array of objects representing all the polygons that are part of the multipolygon.
+        //
+        // Each object has two properties:
+        //     ids - an array of ids of entities that are part of that polygon
+        //     locs - an array of the locations forming the polygon
+        var polygons = entities.multipolygon.reduce(function(polygons, m) {
+            m.multipolygon(graph).forEach(function(group) {
+                group.forEach(function(ring) {
+                    polygons.push({
+                        ids: ring.ids,
+                        locs: ring
+                    });
+                });
+            });
+            return polygons;
+        }, []).concat(entities.closedWay.map(function(d) {
+            return {
+                ids: [d.id],
+                locs: graph.childNodes(d).map(function(n) { return n.loc; })
+            };
+        }));
 
         // contained is an array of arrays of boolean values,
         // where contained[j][k] is true iff the jth way is
@@ -35,15 +48,10 @@ iD.actions.MergePolygon = function(ids) {
         var contained = polygons.map(function(w, i) {
             return polygons.map(function(d, n) {
                 if (i === n) return null;
-                return iD.geo.polygonContainsPolygon(getLocs(d), getLocs(w));
+                return iD.geo.polygonContainsPolygon(d.locs, w.locs);
             });
         });
 
-        function getLocs(way) {
-            return graph.childNodes(way).map(function(d) { return d.loc; });
-        }
-
-
         // Sort all polygons as either outer or inner ways
         var members = [];
             outer = true;
@@ -65,10 +73,12 @@ iD.actions.MergePolygon = function(ids) {
         function extractUncontained(polygons) {
             polygons.forEach(function(d, i) {
                 if (!isContained(d, i)) {
-                    members.push({
-                        type: 'way',
-                        id: d.id,
-                        role: outer ? 'outer' : 'inner'
+                    d.ids.forEach(function(id) {
+                        members.push({
+                            type: 'way',
+                            id: id,
+                            role: outer ? 'outer' : 'inner'
+                        });
                     });
                 }
             });
diff --git a/js/id/core/relation.js b/js/id/core/relation.js
index 13f7dc294..90de844e8 100644
--- a/js/id/core/relation.js
+++ b/js/id/core/relation.js
@@ -169,10 +169,12 @@ _.extend(iD.Relation.prototype, {
             .map(function(m) { return { role: m.role || 'outer', id: m.id, nodes: resolver.childNodes(resolver.entity(m.id)) }; });
 
         function join(ways) {
-            var joined = [], current, first, last, i, how, what;
+            var joined = [], way, current, first, last, i, how, what;
 
             while (ways.length) {
-                current = ways.pop().nodes.slice();
+                way = ways.pop();
+                current = way.nodes.slice();
+                current.ids = [way.id];
                 joined.push(current);
 
                 while (ways.length && _.first(current) !== _.last(current)) {
@@ -206,12 +208,17 @@ _.extend(iD.Relation.prototype, {
                     if (!what)
                         break; // Invalid geometry (unclosed ring)
 
+                    current.ids.push(ways[i].id);
                     ways.splice(i, 1);
                     how.apply(current, what);
                 }
             }
 
-            return joined.map(function(nodes) { return _.pluck(nodes, 'loc'); });
+            return joined.map(function(nodes) {
+                var locs = _.pluck(nodes, 'loc');
+                locs.ids = nodes.ids;
+                return locs;
+            });
         }
 
         function findOuter(inner) {
diff --git a/test/index.html b/test/index.html
index 569ebe82b..c2f9662a1 100644
--- a/test/index.html
+++ b/test/index.html
@@ -110,6 +110,7 @@
     <script src='../js/id/actions/disconnect.js'></script>
     <script src='../js/id/actions/join.js'></script>
     <script src='../js/id/actions/merge.js'></script>
+    <script src='../js/id/actions/merge_polygon.js'></script>
     <script src='../js/id/actions/move_node.js'></script>
     <script src='../js/id/actions/move.js'></script>
     <script src='../js/id/actions/rotate_way.js'></script>