diff --git a/test/built-ins/RegExp/named-groups/groups-object.js b/test/built-ins/RegExp/named-groups/groups-object.js
index a7d2b5433cc..5479db3d8a4 100644
--- a/test/built-ins/RegExp/named-groups/groups-object.js
+++ b/test/built-ins/RegExp/named-groups/groups-object.js
@@ -1,4 +1,5 @@
 // Copyright 2017 Aleksey Shvayka. All rights reserved.
+// Copyright 2017 Mathias Bynens. All rights reserved.
 // This code is governed by the BSD license found in the LICENSE file.
 
 /*---
@@ -8,26 +9,112 @@ esid: sec-regexpbuiltinexec
 features: [regexp-named-groups]
 info: >
   Runtime Semantics: RegExpBuiltinExec ( R, S )
-    24. If R contains any GroupName,
-      a. Let groups be ObjectCreate(null).
-      b. Perform ! CreateDataProperty(A, "groups", groups).
+    24. If _R_ contains any |GroupName|, then
+      a. Let _groups_ be ObjectCreate(*null*).
+    25. Else,
+      a. Let _groups_ be *undefined*.
+    26. Perform ! CreateDataProperty(_A_, `"groups"`, _groups_).
 ---*/
 
-// groups is created with Define, not Set
+// The groups property must be created unconditionally.
+// https://github.com/tc39/proposal-regexp-named-groups/pull/40
+{
+  const re = /./;
+  const result = re.exec("a");
+  assert.sameValue(result.__proto__, Array.prototype);
+  assert(result.hasOwnProperty("groups"));
+  assert.sameValue("a", result[0]);
+  assert.sameValue(0, result.index);
+  assert.sameValue(undefined, result.groups);
+
+  Array.prototype.groups = { a: "b" };
+  assert.sameValue("$<a>", "a".replace(re, "$<a>"));
+  Array.prototype.groups = undefined;
+}
+
+{
+  const re = /(?<a>a).|(?<x>x)/;
+  const result = re.exec("ab");
+  assert.sameValue(result.__proto__, Array.prototype);
+  assert(result.hasOwnProperty("groups"));
+  assert.sameValue("ab", result[0]);
+  assert.sameValue("a", result[1]);
+  assert.sameValue(undefined, result[2]);
+  assert.sameValue(0, result.index);
+  assert.sameValue("a", result.groups.a);
+  assert.sameValue(undefined, result.groups.x);
+
+  // `a` is a matched named capture, `b` is an unmatched named capture, and `z`
+  // is not a named capture.
+  Array.prototype.groups = { a: "b", x: "y", z: "z" };
+  assert.sameValue("a", "ab".replace(re, "$<a>"));
+  assert.sameValue("", "ab".replace(re, "$<x>"));
+  assert.sameValue("", "ab".replace(re, "$<z>"));
+  Array.prototype.groups = undefined;
+}
+
+{
+  class FakeRegExp extends RegExp {
+    exec(subject) {
+      const fakeResult = ["ab", "a"];
+      fakeResult.index = 0;
+      // `groups` is not set, triggering prototype lookup.
+      return fakeResult;
+    }
+  };
+
+  const re = new FakeRegExp();
+  const result = re.exec("ab");
+  assert.sameValue(result.__proto__, Array.prototype);
+  assert.sameValue(false, result.hasOwnProperty("groups"));
+
+  Array.prototype.groups = { a: "b" };
+  Array.prototype.groups.__proto__.b = "c";
+  assert.sameValue("b", "ab".replace(re, "$<a>"));
+  assert.sameValue("c", "ab".replace(re, "$<b>"));
+  Array.prototype.groups = undefined;
+}
+
+{
+  class FakeRegExp extends RegExp {
+    exec(subject) {
+      const fakeResult = ["ab", "a"];
+      fakeResult.index = 0;
+      fakeResult.groups = { a: "b" };
+      fakeResult.groups.__proto__.b = "c";
+      return fakeResult;
+    }
+  };
+
+  const re = new FakeRegExp();
+  const result = re.exec("ab");
+  assert.sameValue(result.__proto__, Array.prototype);
+  assert(result.hasOwnProperty("groups"));
+  assert.sameValue("b", result.groups.a);
+  assert.sameValue("b", "ab".replace(re, "$<a>"));
+  assert.sameValue("c", "ab".replace(re, "$<b>"));
+}
+
+// `groups` is created with Define, not Set.
+// Note: This must be at the bottom of the file, to not interfere with the
+// tests above.
 let counter = 0;
-Object.defineProperty(Array.prototype, "groups", {set() { counter++; }});
+Object.defineProperty(Array.prototype, "groups", {
+  set() { counter++; }
+});
+
 let match = /(?<x>.)/.exec("a");
 assert.sameValue(counter, 0);
 
-// groups is writable, enumerable and configurable
-// (from CreateDataProperty)
+// `groups` is writable, enumerable and configurable
+// (from CreateDataProperty).
 verifyProperty(match, "groups", {
   writable: true,
   enumerable: true,
   configurable: true,
 });
 
-// The '__proto__' property on the groups object is not special,
+// The `__proto__` property on the groups object is not special,
 // and does not affect the [[Prototype]] of the resulting groups object.
 let {groups} = /(?<__proto__>.)/.exec("a");
 assert.sameValue("a", groups.__proto__);