diff --git a/src/conduit/ConduitClient.php b/src/conduit/ConduitClient.php
index 441fe25c..91535ae4 100644
--- a/src/conduit/ConduitClient.php
+++ b/src/conduit/ConduitClient.php
@@ -158,9 +158,11 @@ final class ConduitClient extends Phobject {
     // See T13507. If possible, try to compress requests. To compress requests,
     // we must have "gzencode()" available and the server needs to have
     // asserted it has the "gzip" capability.
-    $can_gzip =
-      (function_exists('gzencode')) &&
-      (isset($this->capabilities['gzip']));
+    // Mozilla: don't compress requests. PHP parses a gzipped
+    // application/x-www-form-urlencoded body as form data before Phabricator
+    // decompresses it, so a large body's stray "&" bytes exceed max_input_vars
+    // and the resulting warning replaces the JSON response.
+    $can_gzip = false;
     if ($can_gzip) {
       $gzip_data = phutil_build_http_querystring($data);
       $gzip_data = gzencode($gzip_data);