diff --git a/declarations/wu.js b/declarations/wu.js
index 0f7e6e1..8d5b6f5 100644
--- a/declarations/wu.js
+++ b/declarations/wu.js
@@ -6,6 +6,8 @@ declare module 'wu' {
     declare export default class Wu<T> {
         static <T>(Iterable<T>): Wu<T>;
 
+        static values<T: Object>(T): Wu<$Values<T>>;
+
         tap(T => mixed): Wu<T>;
 
         map<U>(T => U): Wu<U>;
@@ -24,6 +26,8 @@ declare module 'wu' {
         some(): boolean;
         some(T => boolean): boolean;
 
+        forEach(T => mixed): void;
+
         toArray(): T[];
     }
 }
diff --git a/tests/run.js b/tests/run.js
index 748a7e0..9c2dafe 100644
--- a/tests/run.js
+++ b/tests/run.js
@@ -2,11 +2,12 @@ import * as assert from 'assert';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as yaml from 'yaml-js';
+import wu from 'wu';
 
 import collect from '../src';
 
 function run(title) {
-    let actual, expected;
+    let actual, expected: any;
 
     // Run the collector only if the suite will be checked.
     before(() => {
@@ -14,9 +15,33 @@ function run(title) {
         expected = yaml.load(fs.readFileSync(title + '.yaml', 'utf8'));
     });
 
-    it('should provide expected types', () => {
-        assert.deepEqual((actual: any).types, (expected: any).types);
+    it('should not include cycles', () => {
+        assert.deepEqual(detectCycles(actual.types), new Set);
     });
+
+    it('should provide expected types', () => {
+        assert.deepEqual(actual.types, expected.types);
+    });
+}
+
+function detectCycles(obj: mixed, cycles: Set<mixed> = new Set, objs: Set<mixed> = new Set) {
+    if (obj == null || typeof obj !== 'object') {
+        return cycles;
+    }
+
+    if (objs.has(obj)) {
+        cycles.add(obj);
+    }
+
+    objs.add(obj);
+
+    if (obj instanceof Array) {
+        wu(obj).forEach(item => detectCycles(item, cycles, objs));
+    } else {
+        wu.values(obj).forEach(item => detectCycles(item, cycles, objs));
+    }
+
+    return cycles;
 }
 
 function main() {