diff --git a/lib/blocklib.php b/lib/blocklib.php
index dd8a7bfebf0..be0831f008c 100644
--- a/lib/blocklib.php
+++ b/lib/blocklib.php
@@ -411,7 +411,9 @@ class block_manager {
      */
     public function add_pretend_block($bc, $region) {
         $this->page->initialise_theme_and_output();
-        $this->check_region_is_known($region);
+        if (!$this->is_known_region($region)) {
+            $region = $this->get_default_region();
+        }
         if (array_key_exists($region, $this->visibleblockcontent)) {
             throw new coding_exception('block_manager has already prepared the blocks in region ' .
                     $region . 'for output. It is too late to add a pretend block.');