diff --git a/src/jsonata.js b/src/jsonata.js
index d6198905..19b09409 100644
--- a/src/jsonata.js
+++ b/src/jsonata.js
@@ -922,7 +922,7 @@ var jsonata = (function() {
                 var pair = expr.lhs[pairIndex];
                 var key = yield * evaluate(pair[0], reduce ? item['@'] : item, env);
                 // key has to be a string
-                if (typeof  key !== 'string') {
+                if (typeof  key !== 'string' && key !== undefined) {
                     throw {
                         code: "T1003",
                         stack: (new Error()).stack,
@@ -930,24 +930,27 @@ var jsonata = (function() {
                         value: key
                     };
                 }
-                var entry = {data: item, exprIndex: pairIndex};
-                if (groups.hasOwnProperty(key)) {
-                    // a value already exists in this slot
-                    if(groups[key].exprIndex !== pairIndex) {
-                        // this key has been generated by another expression in this group
-                        // when multiple key expressions evaluate to the same key, then error D1009 must be thrown
-                        throw {
-                            code: "D1009",
-                            stack: (new Error()).stack,
-                            position: expr.position,
-                            value: key
-                        };
-                    }
 
-                    // append it as an array
-                    groups[key].data = fn.append(groups[key].data, item);
-                } else {
-                    groups[key] = entry;
+                if (key !== undefined) {
+                    var entry = {data: item, exprIndex: pairIndex};
+                    if (groups.hasOwnProperty(key)) {
+                        // a value already exists in this slot
+                        if(groups[key].exprIndex !== pairIndex) {
+                            // this key has been generated by another expression in this group
+                            // when multiple key expressions evaluate to the same key, then error D1009 must be thrown
+                            throw {
+                                code: "D1009",
+                                stack: (new Error()).stack,
+                                position: expr.position,
+                                value: key
+                            };
+                        }
+
+                        // append it as an array
+                        groups[key].data = fn.append(groups[key].data, item);
+                    } else {
+                        groups[key] = entry;
+                    }
                 }
             }
         }
diff --git a/test/test-suite/groups/object-constructor/case026.json b/test/test-suite/groups/object-constructor/case026.json
new file mode 100644
index 00000000..b08f49aa
--- /dev/null
+++ b/test/test-suite/groups/object-constructor/case026.json
@@ -0,0 +1,6 @@
+{
+    "expr": "$${id:{'label':label,'value':value}}",
+    "data": [],
+    "bindings": {},
+    "result": {}
+}