diff --git a/js/id/graph/graph.js b/js/id/graph/graph.js
index bd5b87f2e..5e865b9ec 100644
--- a/js/id/graph/graph.js
+++ b/js/id/graph/graph.js
@@ -107,10 +107,12 @@ iD.Graph.prototype = {
         keys = Object.keys(this._parentWays);
         for (i = 0; i < keys.length; i++) {
             child = keys[i];
-            for (k = 0; k < base.parentWays[child].length; k++) {
-                id = base.parentWays[child][k];
-                if (this.entity(id) && !_.contains(this._parentWays[child], id)) {
-                    this._parentWays[child].push(id);
+            if (base.parentWays[child]) {
+                for (k = 0; k < base.parentWays[child].length; k++) {
+                    id = base.parentWays[child][k];
+                    if (this.entity(id) && !_.contains(this._parentWays[child], id)) {
+                        this._parentWays[child].push(id);
+                    }
                 }
             }
         }
@@ -118,10 +120,12 @@ iD.Graph.prototype = {
         keys = Object.keys(this._parentRels);
         for (i = 0; i < keys.length; i++) {
             child = keys[i];
-            for (k = 0; k < base.parentRels[child].length; k++) {
-                id = base.parentRels[child][k];
-                if (this.entity(id) && !_.contains(this._parentRels[child], id)) {
-                    this._parentRels[child].push(id);
+            if (base.parentRels[child]) {
+                for (k = 0; k < base.parentRels[child].length; k++) {
+                    id = base.parentRels[child][k];
+                    if (this.entity(id) && !_.contains(this._parentRels[child], id)) {
+                        this._parentRels[child].push(id);
+                    }
                 }
             }
         }