diff --git a/lib/classes/plugin_manager.php b/lib/classes/plugin_manager.php
index ea6a3293013..00feacac81c 100644
--- a/lib/classes/plugin_manager.php
+++ b/lib/classes/plugin_manager.php
@@ -1651,7 +1651,7 @@ class core_plugin_manager {
         }
 
         // To be able to remove the plugin folder, its parent must be writable, too.
-        if (!is_writable(dirname($pluginfo->rootdir))) {
+        if (!isset($pluginfo->rootdir) || !is_writable(dirname($pluginfo->rootdir))) {
             return false;
         }
 
diff --git a/lib/classes/plugininfo/base.php b/lib/classes/plugininfo/base.php
index 40e20de4686..4eb39a1b188 100644
--- a/lib/classes/plugininfo/base.php
+++ b/lib/classes/plugininfo/base.php
@@ -598,6 +598,10 @@ abstract class base {
     public function get_dir() {
         global $CFG;
 
+        if (!isset($pluginfo->rootdir)) {
+            return '';
+        }
+
         return substr($this->rootdir, strlen($CFG->dirroot));
     }