diff --git a/libraries.api.php b/libraries.api.php
index 8bf95fa..2ebb33f 100644
--- a/libraries.api.php
+++ b/libraries.api.php
@@ -146,9 +146,23 @@
  *     Valid callback groups are:
  *     - info: Callbacks registered in this group are applied after the library
  *       information has been retrieved via hook_libraries_info() or info files.
+ *       At this point the following additional information is available:
+ *       - $library['info type']: How the library information was obtained. Can
+ *         be 'info file', 'module', or 'theme', depending on whether the
+ *         library information was obtained from an info file, an enabled module
+ *         or an enabled theme, respectively.
+ *       Additionally, one of the following three keys is available, depending
+ *       on the value of $library['info type'].
+ *       - $library['info file']: In case the library information was obtained
+ *         from an info file, the URI of the info file.
+ *       - $library['module']: In case the library was obtained from an enabled
+ *         module, the name of the providing module.
+ *       - $library['theme']: In case the library was obtained from an enabled
+ *         theme, the name of the providing theme.
  *     - pre-detect: Callbacks registered in this group are applied after the
  *       library path has been determined and before the version callback is
- *       invoked. At this point the following additional information is available:
+ *       invoked. At this point the following additional information is
+ *       available:
  *       - $library['library path']: The path on the file system to the library.
  *     - post-detect: Callbacks registered in this group are applied after the
  *       library has been successfully detected. At this point the library
diff --git a/libraries.module b/libraries.module
index 0c7a2ce..b14ff1b 100644
--- a/libraries.module
+++ b/libraries.module
@@ -341,27 +341,31 @@ function &libraries_info($name = NULL) {
 
   if (!isset($libraries)) {
     $libraries = array();
-    // Gather information from hook_libraries_info().
+
+    // Gather information from hook_libraries_info() in enabled modules.
     foreach (module_implements('libraries_info') as $module) {
       foreach (module_invoke($module, 'libraries_info') as $machine_name => $properties) {
+        $properties['info type'] = 'module';
         $properties['module'] = $module;
         $libraries[$machine_name] = $properties;
       }
     }
+
     // Gather information from hook_libraries_info() in enabled themes.
-    // @see drupal_alter()
-    global $theme, $base_theme_info;
-    if (isset($theme)) {
-      $theme_keys = array();
-      foreach ($base_theme_info as $base) {
-        $theme_keys[] = $base->name;
-      }
-      $theme_keys[] = $theme;
-      foreach ($theme_keys as $theme_key) {
-        $function = $theme_key . '_' . 'libraries_info';
+    $themes = array();
+    foreach (list_themes() as $theme_name => $theme_info) {
+      if ($theme_info->status && file_exists(drupal_get_path('theme', $theme_name) . '/template.php')) {
+        // Collect a list of viable themes for re-use when calling the alter
+        // hook.
+        $themes[] = $theme_name;
+
+        include_once drupal_get_path('theme', $theme_name) . '/template.php';
+
+        $function = $theme_name . '_libraries_info';
         if (function_exists($function)) {
           foreach ($function() as $machine_name => $properties) {
-            $properties['theme'] = $theme_key;
+            $properties['info type'] = 'theme';
+            $properties['theme'] = $theme_name;
             $libraries[$machine_name] = $properties;
           }
         }
@@ -372,6 +376,7 @@ function &libraries_info($name = NULL) {
     // .info files override module definitions.
     foreach (libraries_scan_info_files() as $machine_name => $file) {
       $properties = drupal_parse_info_file($file->uri);
+      $properties['info type'] = 'info file';
       $properties['info file'] = $file->uri;
       $libraries[$machine_name] = $properties;
     }
@@ -381,8 +386,20 @@ function &libraries_info($name = NULL) {
       libraries_info_defaults($properties, $machine_name);
     }
 
-    // Allow modules to alter the registered libraries.
-    drupal_alter('libraries_info', $libraries);
+    // Allow enabled modules and themes to alter the registered libraries.
+    // drupal_alter() only takes the currently active theme into account, not
+    // all enabled themes.
+    foreach (module_implements('libraries_info_alter') as $module) {
+      $function = $module . '_libraries_info_alter';
+      $function($libraries);
+    }
+    foreach ($themes as $theme) {
+      $function = $theme . '_libraries_info_alter';
+      // The template.php file was included above.
+      if (function_exists($function)) {
+        $function($libraries);
+      }
+    }
 
     // Invoke callbacks in the 'info' group.
     foreach ($libraries as &$properties) {