diff --git a/includes/theme.inc b/includes/theme.inc
index 9e15f21e62452ea6e53fe70b126175a2beb7a592..e7fec486d5a619d1b5e4fa0be4cbb092574808b0 100644
--- a/includes/theme.inc
+++ b/includes/theme.inc
@@ -54,18 +54,8 @@ function init_theme() {
   $base_theme = array();
   $ancestor = $theme;
   while ($ancestor && isset($themes[$ancestor]->base_theme)) {
-    if (isset($themes[$themes[$ancestor]->base_theme])) {
-      $base_theme[] = $new_base_theme = $themes[$themes[$ancestor]->base_theme];
-      // stop if this is final ancestor.
-      if (!isset($new_base_theme->base_theme)) {
-        break;
-      }
-      $ancestor = $new_base_theme->base_theme;
-    }
-    // stop if ancestor didn't exist.
-    else {
-      break;
-    }
+    $base_theme[] = $new_base_theme = $themes[$themes[$ancestor]->base_theme];
+    $ancestor = $themes[$ancestor]->base_theme;
   }
   _init_theme($themes[$theme], array_reverse($base_theme));
 }
@@ -100,21 +90,62 @@ function _init_theme($theme, $base_theme = array()) {
 
   $theme_path = dirname($theme->filename);
 
+  // Prepare stylesheets from this theme as well as all ancestor themes.
+  // We work it this way so that we can have child themes override parent
+  // theme stylesheets easily.
+  $final_stylesheets = array();
+
+  // Grab stylesheets from base theme
+  foreach ($base_theme as $base) {
+    if (!empty($base->stylesheets)) {
+      foreach ($base->stylesheets as $media => $stylesheets) {
+        foreach ($stylesheets as $name => $stylesheet) {
+          $final_stylesheets[$media][$name] = $stylesheet;
+        }
+      }
+    }
+  }
+
   // Add stylesheets used by this theme.
   if (!empty($theme->stylesheets)) {
     foreach ($theme->stylesheets as $media => $stylesheets) {
-      foreach ($stylesheets as $stylesheet) {
-        drupal_add_css($stylesheet, 'theme', $media);
+      foreach ($stylesheets as $name => $stylesheet) {
+        $final_stylesheets[$media][$name] = $stylesheet;
       }
     }
   }
+
+  // And now add the stylesheets properly
+  foreach ($final_stylesheets as $media => $stylesheets) {
+    foreach ($stylesheets as $stylesheet) {
+      drupal_add_css($stylesheet, 'theme', $media);
+    }
+  }
+
+  // Do basically the same as the above for scripts
+  $final_scripts = array();
+
+  // Grab scripts from base theme
+  foreach ($base_theme as $base) {
+    if (!empty($base->scripts)) {
+      foreach ($base->scripts as $name => $script) {
+        $final_scripts[$name] = $script;
+      }
+    }
+  }
+
   // Add scripts used by this theme.
   if (!empty($theme->scripts)) {
-    foreach ($theme->scripts as $script) {
-      drupal_add_js($script, 'theme');
+    foreach ($theme->scripts as $name => $script) {
+      $final_scripts[$name] = $script;
     }
   }
 
+  // Add scripts used by this theme.
+  foreach ($final_scripts as $script) {
+    drupal_add_js($script, 'theme');
+  }
+
   $theme_engine = NULL;
 
   // Initialize the theme.
diff --git a/modules/system/system.admin.inc b/modules/system/system.admin.inc
index 09297e1c4416ec8f98fa74fd564982f4fe7e2634..6ed8e62460f7b697c8c4978c14aa07a8bb076d23 100644
--- a/modules/system/system.admin.inc
+++ b/modules/system/system.admin.inc
@@ -281,6 +281,7 @@ function system_themes_form_submit($form, &$form_state) {
 
   list_themes(TRUE);
   menu_rebuild();
+  drupal_rebuild_theme_registry();
   drupal_set_message(t('The configuration options have been saved.'));
   $form_state['redirect'] = 'admin/build/themes';
 
diff --git a/modules/system/system.module b/modules/system/system.module
index 65d6219b847c1076f3e8303932689d0441b360c5..8827857e8856e7657fc6767809e4417c683366f4 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -742,28 +742,6 @@ function system_theme_data() {
         $themes[$key]->prefix = $key;
       }
     }
-    // Add any stylesheets from the base theme, unless the names match in which case
-    // the sub-theme wins. Note that we slip the base theme's stylesheets in at the
-    // beginning of the array so that they get added to the page in the correct order.
-    foreach ($themes[$base_key]->info['stylesheets'] as $media => $stylesheets) {
-      foreach ($stylesheets as $stylesheet => $path) {
-        if (!isset($themes[$key]->info['stylesheets'][$media][$stylesheet])) {
-          // We need to ensure the media array exists, or the array addition below doesn't work.
-          if (!isset($themes[$key]->info['stylesheets'][$media])) {
-            $themes[$key]->info['stylesheets'][$media] = array();
-          }
-          $themes[$key]->info['stylesheets'][$media] = array($stylesheet => $path) + $themes[$key]->info['stylesheets'][$media];
-        }
-      }
-    }
-    // Add any scripts from the base theme, unless the names match in which case
-    // the sub-theme wins. Note that we slip the base theme's scripts in at the
-    // beginning of the array so that they get added to the page in the correct order.
-    foreach ($themes[$base_key]->info['scripts'] as $script => $path) {
-      if (!isset($themes[$key]->info['scripts'][$script])) {
-        $themes[$key]->info['scripts'] = array($script => $path) + $themes[$key]->info['scripts'];
-      }
-    }
   }
 
   // Extract current files from database.
@@ -798,7 +776,7 @@ function system_find_base_theme($themes, $key, $used_keys = array()) {
   // Is the base theme itself a child of another theme?
   if (isset($themes[$base_key]->info['base theme'])) {
     // Prevent loops.
-    if ($used_keys[$base_key]) {
+    if (!empty($used_keys[$base_key])) {
       return NULL;
     }
     $used_keys[$base_key] = TRUE;