diff --git a/modules/osm/entity.js b/modules/osm/entity.js
index 7212443de..5636fdc78 100644
--- a/modules/osm/entity.js
+++ b/modules/osm/entity.js
@@ -36,7 +36,11 @@ osmEntity.id.fromOSM = function(type, id) {
 
 
 osmEntity.id.toOSM = function(id) {
-    return id.slice(1);
+    var match = id.match(/^[cnwr](-?\d+)$/);
+    if (match) {
+        return match[1];
+    }
+    return '';
 };
 
 
@@ -129,7 +133,8 @@ osmEntity.prototype = {
 
 
     isNew: function() {
-        return this.osmId() < 0;
+        var osmId = osmEntity.id.toOSM(this.id);
+        return osmId.length === 0 || osmId[0] === '-';
     },
 
 
diff --git a/test/spec/osm/entity.js b/test/spec/osm/entity.js
index cbc81833d..95f440c9a 100644
--- a/test/spec/osm/entity.js
+++ b/test/spec/osm/entity.js
@@ -32,6 +32,11 @@ describe('iD.osmEntity', function () {
         describe('.toOSM', function () {
             it('reverses fromOSM', function () {
                 expect(iD.osmEntity.id.toOSM(iD.osmEntity.id.fromOSM('node', '1'))).to.equal('1');
+                expect(iD.osmEntity.id.toOSM(iD.osmEntity.id.fromOSM('node', '-1'))).to.equal('-1');
+            });
+
+            it('returns the empty string for other strings', function () {
+                expect(iD.osmEntity.id.toOSM('a')).to.equal('');
             });
         });
     });