diff --git a/src/Composer/Installer/InstallationManager.php b/src/Composer/Installer/InstallationManager.php
index 06e8d65b9..9e55c4ac7 100644
--- a/src/Composer/Installer/InstallationManager.php
+++ b/src/Composer/Installer/InstallationManager.php
@@ -184,6 +184,8 @@ class InstallationManager
         $runCleanup = function () use (&$cleanupPromises, $loop) {
             $promises = array();
 
+            $loop->abortJobs();
+
             foreach ($cleanupPromises as $cleanup) {
                 $promises[] = new \React\Promise\Promise(function ($resolve, $reject) use ($cleanup) {
                     $promise = $cleanup();
diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index 365caf899..257a29115 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -23,6 +23,7 @@ use Composer\Util\HttpDownloader;
 use React\Promise\Promise;
 
 /**
+ * @internal
  * @author Jordi Boggiano <j.boggiano@seld.be>
  * @author Nicolas Grekas <p@tchwork.com>
  */
@@ -90,6 +91,9 @@ class CurlDownloader
         $this->authHelper = new AuthHelper($io, $config);
     }
 
+    /**
+     * @return int internal job id
+     */
     public function download($resolve, $reject, $origin, $url, $options, $copyTo = null)
     {
         $attributes = array();
@@ -101,6 +105,9 @@ class CurlDownloader
         return $this->initDownload($resolve, $reject, $origin, $url, $options, $copyTo, $attributes);
     }
 
+    /**
+     * @return int internal job id
+     */
     private function initDownload($resolve, $reject, $origin, $url, $options, $copyTo = null, array $attributes = array())
     {
         $attributes = array_merge(array(
@@ -199,8 +206,29 @@ class CurlDownloader
         }
 
         $this->checkCurlResult(curl_multi_add_handle($this->multiHandle, $curlHandle));
-// TODO progress
+        // TODO progress
         //$params['notification'](STREAM_NOTIFY_RESOLVE, STREAM_NOTIFY_SEVERITY_INFO, '', 0, 0, 0, false);
+
+        return (int) $curlHandle;
+    }
+
+    public function abortRequest($id)
+    {
+        if (isset($this->jobs[$id]) && isset($this->jobs[$id]['handle'])) {
+            $job = $this->jobs[$id];
+            curl_multi_remove_handle($this->multiHandle, $job['handle']);
+            curl_close($job['handle']);
+            if (is_resource($job['headerHandle'])) {
+                fclose($job['headerHandle']);
+            }
+            if (is_resource($job['bodyHandle'])) {
+                fclose($job['bodyHandle']);
+            }
+            if ($job['filename']) {
+                @unlink($job['filename'].'~');
+            }
+            unset($this->jobs[$id]);
+        }
     }
 
     public function tick()
@@ -235,7 +263,7 @@ class CurlDownloader
             $statusCode = null;
             $response = null;
             try {
-// TODO progress
+                // TODO progress
                 //$this->onProgress($curlHandle, $job['callback'], $progress, $job['progress']);
                 if (CURLE_OK !== $errno || $error) {
                     throw new TransportException($error);
@@ -285,8 +313,6 @@ class CurlDownloader
                 // fail 4xx and 5xx responses and capture the response
                 if ($statusCode >= 400 && $statusCode <= 599) {
                     throw $this->failResponse($job, $response, $response->getStatusMessage());
-// TODO progress
-//                        $this->io->overwriteError("Downloading (<error>failed</error>)", false);
                 }
 
                 if ($job['attributes']['storeAuth']) {
diff --git a/src/Composer/Util/HttpDownloader.php b/src/Composer/Util/HttpDownloader.php
index 41ced41e3..6fe53390e 100644
--- a/src/Composer/Util/HttpDownloader.php
+++ b/src/Composer/Util/HttpDownloader.php
@@ -31,6 +31,7 @@ class HttpDownloader
     const STATUS_STARTED = 2;
     const STATUS_COMPLETED = 3;
     const STATUS_FAILED = 4;
+    const STATUS_ABORTED = 5;
 
     private $io;
     private $config;
@@ -184,8 +185,20 @@ class HttpDownloader
 
         $downloader = $this;
         $io = $this->io;
+        $curl = $this->curl;
 
-        $canceler = function () {};
+        $canceler = function () use (&$job, $curl) {
+            if ($job['status'] === self::STATUS_QUEUED) {
+                $job['status'] = self::STATUS_ABORTED;
+            }
+            if ($job['status'] !== self::STATUS_STARTED) {
+                return;
+            }
+            $job['status'] = self::STATUS_ABORTED;
+            if (isset($job['curl_id'])) {
+                $curl->abortRequest($job['curl_id']);
+            }
+        };
 
         $promise = new Promise($resolver, $canceler);
         $promise->then(function ($response) use (&$job, $downloader) {
@@ -242,9 +255,9 @@ class HttpDownloader
         }
 
         if ($job['request']['copyTo']) {
-            $this->curl->download($resolve, $reject, $origin, $url, $options, $job['request']['copyTo']);
+            $job['curl_id'] = $this->curl->download($resolve, $reject, $origin, $url, $options, $job['request']['copyTo']);
         } else {
-            $this->curl->download($resolve, $reject, $origin, $url, $options);
+            $job['curl_id'] = $this->curl->download($resolve, $reject, $origin, $url, $options);
         }
     }
 
@@ -294,14 +307,11 @@ class HttpDownloader
         }
 
         if (null !== $index) {
-            if ($this->jobs[$index]['status'] === self::STATUS_COMPLETED || $this->jobs[$index]['status'] === self::STATUS_FAILED) {
-                return false;
-            }
-            return true;
+            return $this->jobs[$index]['status'] < self::STATUS_COMPLETED;
         }
 
         foreach ($this->jobs as $job) {
-            if (!in_array($job['status'], array(self::STATUS_COMPLETED, self::STATUS_FAILED), true)) {
+            if ($job['status'] < self::STATUS_COMPLETED) {
                 return true;
             } elseif (!$job['sync']) {
                 unset($this->jobs[$job['id']]);
diff --git a/src/Composer/Util/Loop.php b/src/Composer/Util/Loop.php
index b0061ba2d..b7382f1ed 100644
--- a/src/Composer/Util/Loop.php
+++ b/src/Composer/Util/Loop.php
@@ -76,4 +76,13 @@ class Loop
             throw $uncaught;
         }
     }
+
+    public function abortJobs()
+    {
+        if ($this->currentPromises) {
+            foreach ($this->currentPromises as $promise) {
+                $promise->cancel();
+            }
+        }
+    }
 }
diff --git a/src/Composer/Util/ProcessExecutor.php b/src/Composer/Util/ProcessExecutor.php
index b443e541d..59db0c0c0 100644
--- a/src/Composer/Util/ProcessExecutor.php
+++ b/src/Composer/Util/ProcessExecutor.php
@@ -281,15 +281,11 @@ class ProcessExecutor
         }
 
         if (null !== $index) {
-            if ($this->jobs[$index]['status'] === self::STATUS_COMPLETED || $this->jobs[$index]['status'] === self::STATUS_FAILED || $this->jobs[$index]['status'] === self::STATUS_ABORTED) {
-                return false;
-            }
-
-            return true;
+            return $this->jobs[$index]['status'] < self::STATUS_COMPLETED;
         }
 
         foreach ($this->jobs as $job) {
-            if (!in_array($job['status'], array(self::STATUS_COMPLETED, self::STATUS_FAILED, self::STATUS_ABORTED), true)) {
+            if ($job['status'] < self::STATUS_COMPLETED) {
                 return true;
             } else {
                 unset($this->jobs[$job['id']]);
diff --git a/src/Composer/Util/RemoteFilesystem.php b/src/Composer/Util/RemoteFilesystem.php
index b0dfbea94..4bac6a88f 100644
--- a/src/Composer/Util/RemoteFilesystem.php
+++ b/src/Composer/Util/RemoteFilesystem.php
@@ -20,6 +20,7 @@ use Composer\Util\HttpDownloader;
 use Composer\Util\Http\Response;
 
 /**
+ * @internal
  * @author François Pluchino <francois.pluchino@opendisplay.com>
  * @author Jordi Boggiano <j.boggiano@seld.be>
  * @author Nils Adermann <naderman@naderman.de>