diff --git a/src/polymer-expressions.js b/src/polymer-expressions.js
index 953ce65..11448d3 100644
--- a/src/polymer-expressions.js
+++ b/src/polymer-expressions.js
@@ -194,6 +194,7 @@
     this.depsList = [];
     this.currentPath = undefined;
     this.ident = undefined;
+    this.indexName = undefined;
   }
 
   ASTDelegate.prototype = {
@@ -314,9 +315,10 @@
       this.ident = ident;
     },
 
-    createInExpression: function(ident, expression) {
+    createInExpression: function(ident, indexName, expression) {
       this.expression = expression;
       this.ident = ident;
+      this.indexName = indexName;
     },
 
     createTopLevel: function(expression) {
diff --git a/tests/tests.js b/tests/tests.js
index ba6a5f5..831962a 100644
--- a/tests/tests.js
+++ b/tests/tests.js
@@ -862,4 +862,29 @@ suite('PolymerExpressions', function() {
     Platform.performMicrotaskCheckpoint();
     assert.equal('B', div.childNodes[1].textContent);
   });
+
+  test('in expression with index scope', function() {
+    var div = createTestHtml(
+        '<template repeat="{{ user, index in array }}">' +
+            '{{ index }}. {{ user }}' +
+        '</template>');
+
+    var model = {
+      array: ['a', 'b']
+    };
+
+    recursivelySetTemplateModel(div, model);
+    Platform.performMicrotaskCheckpoint();
+
+    // TODO(arv): Enable the rest of this test when we have hooked up the
+    // binding for the index.
+    // assert.strictEqual('0. a', div.childNodes[1].textContent);
+    // assert.strictEqual('1. b', div.childNodes[2].textContent);
+
+    // model.array.splice(1, 0, 'c');
+    // Platform.performMicrotaskCheckpoint();
+    // assert.strictEqual('0. a', div.childNodes[1].textContent);
+    // assert.strictEqual('1. c', div.childNodes[2].textContent);
+    // assert.strictEqual('2. b', div.childNodes[3].textContent);
+  });
 });
diff --git a/third_party/esprima/esprima.js b/third_party/esprima/esprima.js
index b113fe8..e8df13d 100644
--- a/third_party/esprima/esprima.js
+++ b/third_party/esprima/esprima.js
@@ -971,6 +971,7 @@
     //   Expression as Identifier
 
     // InExpression ::
+    //   Identifier, Identifier in Expression
     //   Identifier in Expression
 
     function parseTopLevel() {
@@ -981,7 +982,7 @@
         if (expr) {
             if (lookahead.value === 'as') {
                 parseAsExpression(expr);
-            } else if (lookahead.value === 'in' &&
+            } else if (lookahead.value === ',' || lookahead.value == 'in' &&
                        expr.type === Syntax.Identifier) {
                 parseInExpression(expr);
             } else if (match('|')) {
@@ -1034,9 +1035,17 @@
     }
 
     function parseInExpression(identifier) {
+        var indexName;
+        if (lookahead.value === ',') {
+            lex();
+            if (lookahead.type !== Token.Identifier)
+                throwUnexpected(lookahead);
+            indexName = lex().value;
+        }
+
         lex();  // in
         var expr = parseExpression();
-        delegate.createInExpression(identifier.name, expr);
+        delegate.createInExpression(identifier.name, indexName, expr);
     }
 
     function parse(code, inDelegate) {