diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 3bcfa85..06f5571 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1916,13 +1916,11 @@ function system_update_8015() {
   };
 
   // It is possible that version information already exists. For example,
-  // another hook_update_N hook could have installed a module. Do not overwrite
-  // existing data.
-  $versions = \Drupal\Component\Utility\NestedArray::mergeDeep(
-    array_map($map_version_info, \Drupal::moduleHandler()->getModuleList()),
-    array_map($map_version_info, \Drupal::service('theme_handler')->listInfo()),
-    $versions
-  );
+  // another hook_update_N hook could have installed a module. However we can
+  // safely ignore that as this will ensure that all the information is correct
+  // at the time of writing.
+  $versions = array_map($map_version_info, \Drupal::moduleHandler()->getModuleList()) +
+    array_map($map_version_info, \Drupal::service('theme_handler')->listInfo());
   ksort($versions);
   $core->set('versions', $versions)->save();
 }