diff --git a/src/aphront/AphrontRequest.php b/src/aphront/AphrontRequest.php
--- a/src/aphront/AphrontRequest.php
+++ b/src/aphront/AphrontRequest.php
@@ -931,13 +931,14 @@
       }
     }
 
-    foreach ($headers as $header) {
-      list($key, $value) = $header;
-      switch ($key) {
-        case 'Host':
-        case 'Authorization':
+    foreach ($headers as $header_key => $header) {
+      list($header_head, $header_body) = $header;
+      $header_head = phutil_utf8_strtolower($header_head);
+      switch ($header_head) {
+        case 'host':
+        case 'authorization':
           // Don't forward these headers, we've already handled them elsewhere.
-          unset($headers[$key]);
+          unset($headers[$header_key]);
           break;
         default:
           break;