diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 0fe33db..03048d4 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -429,6 +429,12 @@ function install_begin_request($class_loader, &$install_state) {
     drupal_get_filename('profile', $name, $profile->getPathname());
   }
 
+  // Before having installed the system module and being able to do a module
+  // rebuild, prime the drupal_get_filename() static cache with the module's
+  // exact location.
+  // @todo Remove as part of https://www.drupal.org/node/2186491
+  drupal_get_filename('module', 'system', 'core/modules/system/system.info.yml');
+
   if ($profile = _install_select_profile($install_state)) {
     $install_state['parameters']['profile'] = $profile;
     install_load_profile($install_state);
diff --git a/core/lib/Drupal/Core/Extension/ExtensionList.php b/core/lib/Drupal/Core/Extension/ExtensionList.php
index e9d627e..a7cc21d 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionList.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionList.php
@@ -142,7 +142,10 @@ public function reset() {
     $this->fileNames = NULL;
     $this->state->delete($this->getFilenameCacheId());
     $this->cache->delete($this->getFilenameCacheId());
-    $this->addedFileNames = [];
+    // We explicitly don't reset the addedFileNames as its sort of a static
+    // cache.
+    // @todo On the longrun it would be great to add the reset, but the early
+    //   installer fails due to that.
     return $this;
   }