diff --git a/src/ArrayCache.php b/src/ArrayCache.php
index 03dcc15..ff2a06d 100644
--- a/src/ArrayCache.php
+++ b/src/ArrayCache.php
@@ -20,10 +20,12 @@ public function get($key)
     public function set($key, $value)
     {
         $this->data[$key] = $value;
+        return new Promise\FulfilledPromise(true);
     }
 
     public function remove($key)
     {
         unset($this->data[$key]);
+        return new Promise\FulfilledPromise(true);
     }
 }
diff --git a/src/CacheInterface.php b/src/CacheInterface.php
index fd5f2d5..34211a2 100644
--- a/src/CacheInterface.php
+++ b/src/CacheInterface.php
@@ -2,12 +2,22 @@
 
 namespace React\Cache;
 
+use React\Promise\PromiseInterface;
+
 interface CacheInterface
 {
-    // @return React\Promise\PromiseInterface
+    /**
+     * @return PromiseInterface
+     */
     public function get($key);
 
+    /**
+     * @return PromiseInterface
+     */
     public function set($key, $value);
 
+    /**
+     * @return PromiseInterface
+     */
     public function remove($key);
 }
diff --git a/tests/ArrayCacheTest.php b/tests/ArrayCacheTest.php
index eec3739..383490b 100644
--- a/tests/ArrayCacheTest.php
+++ b/tests/ArrayCacheTest.php
@@ -6,6 +6,9 @@
 
 class ArrayCacheTest extends TestCase
 {
+    /**
+     * @var ArrayCache
+     */
     private $cache;
 
     public function setUp()
@@ -27,9 +30,17 @@ public function getShouldRejectPromiseForNonExistentKey()
     /** @test */
     public function setShouldSetKey()
     {
-        $this->cache
+        $setPromise = $this->cache
             ->set('foo', 'bar');
 
+        $mock = $this->createCallableMock();
+        $mock
+            ->expects($this->once())
+            ->method('__invoke')
+            ->with($this->identicalTo(true));
+
+        $setPromise->then($mock);
+
         $success = $this->createCallableMock();
         $success
             ->expects($this->once())
@@ -47,9 +58,17 @@ public function removeShouldRemoveKey()
         $this->cache
             ->set('foo', 'bar');
 
-        $this->cache
+        $removePromise = $this->cache
             ->remove('foo');
 
+        $mock = $this->createCallableMock();
+        $mock
+            ->expects($this->once())
+            ->method('__invoke')
+            ->with($this->identicalTo(true));
+
+        $removePromise->then($mock);
+
         $this->cache
             ->get('foo')
             ->then(