diff --git a/mod/lti/service.php b/mod/lti/service.php
index fad61e64407..b96f566294e 100644
--- a/mod/lti/service.php
+++ b/mod/lti/service.php
@@ -33,7 +33,7 @@ use moodle\mod\lti as lti;
 
 $rawbody = file_get_contents("php://input");
 
-foreach (getallheaders() as $name => $value) {
+foreach (lti\OAuthUtil::get_headers() as $name => $value) {
     if ($name === 'Authorization') {
         // TODO: Switch to core oauthlib once implemented - MDL-30149
         $oauthparams = lti\OAuthUtil::split_header($value);