diff --git a/chai/chai-tests.ts b/chai/chai-tests.ts
index 98d75e8aef..ddaa84ee28 100644
--- a/chai/chai-tests.ts
+++ b/chai/chai-tests.ts
@@ -337,6 +337,11 @@ function deepEqual3(Date) {
     expect(a).not.to.deep.equal({});
 }
 
+function deepInclude(val) {
+    expect(['foo', 'bar']).to.deep.include(['bar', 'foo']);
+    expect(['foo', 'bar']).not.to.deep.equal(['foo', 'baz' ]);
+}
+
 function empty() {
     function FakeArgs() { };
     FakeArgs.prototype.length = 0;
diff --git a/chai/chai.d.ts b/chai/chai.d.ts
index 4b9d313dd2..dd0adf9740 100644
--- a/chai/chai.d.ts
+++ b/chai/chai.d.ts
@@ -132,6 +132,7 @@ declare module chai {
 
     interface Deep {
         equal: Equal;
+        include: Include;
         property: Property;
     }