diff --git a/src/conduit/ConduitClient.php b/src/conduit/ConduitClient.php
--- a/src/conduit/ConduitClient.php
+++ b/src/conduit/ConduitClient.php
@@ -143,12 +143,25 @@
 
     // Always use the cURL-based HTTPSFuture, for proxy support and other
     // protocol edge cases that HTTPFuture does not support.
-    $core_future = new HTTPSFuture($uri, $data);
+    $core_future = new HTTPSFuture($uri);
     $core_future->addHeader('Host', $this->getHostStringForHeader());
 
     $core_future->setMethod('POST');
     $core_future->setTimeout($this->timeout);
 
+    // See T13507. If possible, try to compress requests. We always expect
+    // Phabricator to be able to accept "Content-Encoding: gzip" requests.
+    $can_gzip = function_exists('gzencode');
+    if ($can_gzip) {
+      $gzip_data = phutil_build_http_querystring($data);
+      $gzip_data = gzencode($gzip_data);
+
+      $core_future->addHeader('Content-Encoding', 'gzip');
+      $core_future->setData($gzip_data);
+    } else {
+      $core_future->setData($data);
+    }
+
     if ($this->username !== null) {
       $core_future->setHTTPBasicAuthCredentials(
         $this->username,