diff --git a/README.md b/README.md
index 8ccaf89..2545cda 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,8 @@ This example fetches the value of the key `foo` and passes it to the
 `var_dump` function. You can use any of the composition provided by
 [promises](https://github.com/reactphp/promise).
 
-If the key `foo` does not exist, the promise will be fulfilled with `null` as value.
+If the key `foo` does not exist, the promise will be fulfilled with `null` as value. On 
+any error it will also resolve with `null`.
 
 #### set()
 
@@ -56,8 +57,9 @@ $cache->set('foo', 'bar');
 ```
 
 This example eventually sets the value of the key `foo` to `bar`. If it
-already exists, it is overridden. No guarantees are made as to when the cache
-value is set. If the cache implementation has to go over the network to store
+already exists, it is overridden. To provide guarantees as to when the cache
+value is set a promise is returned. The promise will fulfill with `true` on success 
+or `false` on error. If the cache implementation has to go over the network to store 
 it, it may take a while.
 
 #### remove()
@@ -67,7 +69,8 @@ $cache->remove('foo');
 ```
 
 This example eventually removes the key `foo` from the cache. As with `set`,
-this may not happen instantly.
+this may not happen instantly and a promise is returned to provide guarantees whether 
+or not the item has been removed from cache.
 
 ### ArrayCache
 
diff --git a/src/ArrayCache.php b/src/ArrayCache.php
index 6da1574..f4bf9e8 100644
--- a/src/ArrayCache.php
+++ b/src/ArrayCache.php
@@ -11,7 +11,7 @@ class ArrayCache implements CacheInterface
     public function get($key)
     {
         if (!isset($this->data[$key])) {
-            return Promise\resolve(null);
+            return Promise\resolve();
         }
 
         return Promise\resolve($this->data[$key]);
@@ -20,10 +20,12 @@ public function get($key)
     public function set($key, $value)
     {
         $this->data[$key] = $value;
+        return Promise\resolve(true);
     }
 
     public function remove($key)
     {
         unset($this->data[$key]);
+        return Promise\resolve(true);
     }
 }
diff --git a/src/CacheInterface.php b/src/CacheInterface.php
index c4f5a2f..da6661f 100644
--- a/src/CacheInterface.php
+++ b/src/CacheInterface.php
@@ -8,7 +8,7 @@ interface CacheInterface
 {
     /**
      * Retrieve an item from the cache, resolves with its value on
-     * success or null when no item can be found.
+     * success or null when no item can be found or when an error occurs.
      *
      * @param string $key
      * @return PromiseInterface
@@ -16,19 +16,22 @@ interface CacheInterface
     public function get($key);
 
     /**
-     * Store an item in the cache.
+     * Store an item in the cache, returns a promise which resolves to true on success or
+     * false on error.
      *
      * @param string $key
      * @param mixed $value
-     * @return void
+     * @return PromiseInterface Returns a promise which resolves to true on success of false on error
      */
     public function set($key, $value);
 
     /**
-     * Remove an item from the cache.
+     * Remove an item from the cache, returns a promise which resolves to true on success or
+     * false on error. When the $key isn't found in the cache it also
+     * resolves true.
      *
      * @param string $key
-     * @return void
+     * @return PromiseInterface Returns a promise which resolves to true on success of false on error
      */
     public function remove($key);
 }
diff --git a/tests/ArrayCacheTest.php b/tests/ArrayCacheTest.php
index 9ebed3c..f98fc0e 100644
--- a/tests/ArrayCacheTest.php
+++ b/tests/ArrayCacheTest.php
@@ -6,6 +6,9 @@
 
 class ArrayCacheTest extends TestCase
 {
+    /**
+     * @var ArrayCache
+     */
     private $cache;
 
     public function setUp()
@@ -33,9 +36,17 @@ public function getShouldResolvePromiseWithNullForNonExistentKey()
     /** @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())
@@ -53,9 +64,17 @@ 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(