diff --git a/src/Composer/Util/Http/CurlDownloader.php b/src/Composer/Util/Http/CurlDownloader.php
index 577c81b47..1cdae6df9 100644
--- a/src/Composer/Util/Http/CurlDownloader.php
+++ b/src/Composer/Util/Http/CurlDownloader.php
@@ -34,6 +34,14 @@ use Symfony\Component\HttpFoundation\IpUtils;
  */
 class CurlDownloader
 {
+    /**
+     * Known libcurl's broken versions when proxy is in use with HTTP/2
+     * multiplexing.
+     *
+     * @var list<non-empty-string>
+     */
+    private const BAD_MULTIPLEXING_CURL_VERSIONS = ['7.87.0', '7.88.0', '7.88.1'];
+
     /** @var \CurlMultiHandle */
     private $multiHandle;
     /** @var \CurlShareHandle */
@@ -99,7 +107,18 @@ class CurlDownloader
 
         $this->multiHandle = $mh = curl_multi_init();
         if (function_exists('curl_multi_setopt')) {
-            curl_multi_setopt($mh, CURLMOPT_PIPELINING, \PHP_VERSION_ID >= 70400 ? /* CURLPIPE_MULTIPLEX */ 2 : /*CURLPIPE_HTTP1 | CURLPIPE_MULTIPLEX*/ 3);
+            if (ProxyManager::getInstance()->hasProxy() && ($version = curl_version()) !== false && in_array($version['version'], self::BAD_MULTIPLEXING_CURL_VERSIONS, true)) {
+                /**
+                 * Disable HTTP/2 multiplexing for some broken versions of libcurl.
+                 *
+                 * In certain versions of libcurl when proxy is in use with HTTP/2
+                 * multiplexing, connections will continue stacking up. This was
+                 * fixed in libcurl 8.0.0 in curl/curl@821f6e2a89de8aec1c7da3c0f381b92b2b801efc
+                 */
+                curl_multi_setopt($mh, CURLMOPT_PIPELINING, /* CURLPIPE_NOTHING */ 0);
+            } else {
+                curl_multi_setopt($mh, CURLMOPT_PIPELINING, \PHP_VERSION_ID >= 70400 ? /* CURLPIPE_MULTIPLEX */ 2 : /*CURLPIPE_HTTP1 | CURLPIPE_MULTIPLEX*/ 3);
+            }
             if (defined('CURLMOPT_MAX_HOST_CONNECTIONS') && !defined('HHVM_VERSION')) {
                 curl_multi_setopt($mh, CURLMOPT_MAX_HOST_CONNECTIONS, 8);
             }
diff --git a/src/Composer/Util/Http/ProxyManager.php b/src/Composer/Util/Http/ProxyManager.php
index 247105fa5..09d061bb4 100644
--- a/src/Composer/Util/Http/ProxyManager.php
+++ b/src/Composer/Util/Http/ProxyManager.php
@@ -59,6 +59,11 @@ class ProxyManager
         self::$instance = null;
     }
 
+    public function hasProxy(): bool
+    {
+        return $this->httpProxy !== null && $this->httpsProxy !== null;
+    }
+
     /**
      * Returns a RequestProxy instance for the request url
      *