diff --git a/src/Controller/PluginRevisionController.php b/src/Controller/PluginRevisionController.php
index b266591..d7cfc70 100644
--- a/src/Controller/PluginRevisionController.php
+++ b/src/Controller/PluginRevisionController.php
@@ -263,7 +263,7 @@ class PluginRevisionController extends ControllerBase {
       ];
       $i = 0;
       // Find the previous revision.
-      while ($left_revision_id > $revision_ids[$i]) {
+      while (isset($revision_ids[$i]) && $left_revision_id > $revision_ids[$i]) {
         $i += 1;
       }
       if ($i != 0) {