diff --git a/webservice/rest/locallib.php b/webservice/rest/locallib.php
index 49f0c6d1040..bf6e0700de2 100644
--- a/webservice/rest/locallib.php
+++ b/webservice/rest/locallib.php
@@ -112,7 +112,10 @@ class webservice_rest_server extends webservice_base_server {
         //Check that the returned values are valid
         try {
             if ($this->function->returns_desc != null) {
-                $validatedvalues = external_api::clean_returnvalue($this->function->returns_desc, $this->returns);
+                $validatedvalues = \core_external\external_api::clean_returnvalue(
+                    $this->function->returns_desc,
+                    $this->returns
+                );
             } else {
                 $validatedvalues = null;
             }