--- devel.module
+++ (clipboard)
@@ -615,13 +615,16 @@
 }
 
 function devel_block_switch_user() {
-  $links = devel_switch_user_list();
-  if (!empty($links)) {
-    $block['subject'] = t('Switch user');
-    $build['devel_links'] = array('#theme' => 'links', '#links' => $links);
-    $build['devel_form'] = drupal_get_form('devel_switch_user_form');
-    $block['content'] = $build;
-    return $block;
+  if (user_access('switch users')) {
+    $list_size = variable_get('devel_switch_user_list_size', 10);
+    $links = devel_switch_user_list();
+    if (!empty($links) or $list_size == 0) {
+      $block['subject'] = t('Switch user');
+      $build['devel_links'] = array('#theme' => 'links', '#links' => $links);
+      $build['devel_form'] = drupal_get_form('devel_switch_user_form');
+      $block['content'] = $build;
+      return $block;
+    }
   }
 }