diff --git a/auto-complete.el b/auto-complete.el
index b600c2c..8b44a80 100644
--- a/auto-complete.el
+++ b/auto-complete.el
@@ -164,10 +164,11 @@
   :type 'integer
   :group 'auto-complete)
 
-(defcustom ac-quick-help-prefer-x t
-  "Prefer X tooltip than overlay popup for displaying quick help."
+(defcustom ac-quick-help-prefer-pos-tip t
+  "Prefer native tooltip with pos-tip than overlay popup for displaying quick help."
   :type 'boolean
   :group 'auto-complete)
+(defvaralias 'ac-quick-help-prefer-x 'ac-quick-help-prefer-pos-tip)
 
 (defcustom ac-candidate-limit nil
   "Limit number of candidates. Non-integer means no limit."
@@ -1243,15 +1244,18 @@ that have been made before in this function."
             (pos-tip-hide))
           t)))))
 
+(defun ac-quick-help-use-pos-tip-p ()
+  (and ac-quick-help-prefer-pos-tip
+       window-system
+       (featurep 'pos-tip)))
+
 (defun ac-quick-help (&optional force)
   (interactive)
   (when (and (or force (null this-command))
              (ac-menu-live-p)
              (null ac-quick-help))
       (setq ac-quick-help
-            (funcall (if (and ac-quick-help-prefer-x
-                              (eq window-system 'x)
-                              (featurep 'pos-tip))
+            (funcall (if (ac-quick-help-use-pos-tip-p)
                          'ac-pos-tip-show-quick-help
                        'popup-menu-show-quick-help)
                      ac-menu nil
@@ -1272,9 +1276,7 @@ that have been made before in this function."
     (let ((doc (popup-item-documentation (cdr ac-last-completion)))
           (point (marker-position (car ac-last-completion))))
       (when (stringp doc)
-        (if (and ac-quick-help-prefer-x
-                 (eq window-system 'x)
-                 (featurep 'pos-tip))
+        (if (ac-quick-help-use-pos-tip-p)
             (with-no-warnings (pos-tip-show doc nil point nil 0))
           (popup-tip doc
                      :point point
diff --git a/doc/changes.ja.txt b/doc/changes.ja.txt
index 9f2c522..1f32f25 100644
--- a/doc/changes.ja.txt
+++ b/doc/changes.ja.txt
@@ -32,6 +32,7 @@ v1.4の変更点 {#Changes_v1.4}
 * 頻度計算で稀に起こるエラー
 * 辞書のキャッシュ戦略の改善
 * help-modeがおかしくなる問題を修正 ("help-setup-xref: Symbol's value as variable is void: help-xref-following")
+* auto-completeがWindows上でpos-tipを使えなかった問題を修正
 
 v1.3.1の変更点 {#Changes_v1.3.1}
 ------------
diff --git a/doc/changes.txt b/doc/changes.txt
index 9a34f4d..d6e4d85 100644
--- a/doc/changes.txt
+++ b/doc/changes.txt
@@ -32,6 +32,7 @@ v1.4 Changes {#Changes_v1.4}
 * Rare completion frequency computation error
 * Improve dictionary caching sterategy
 * Fixed help-mode error ("help-setup-xref: Symbol's value as variable is void: help-xref-following")
+* Fixed auto-complete couldn't use pos-tip on Windows
 
 v1.3.1 Changes {#Changes_v1.3.1}
 ------------
diff --git a/doc/manual.ja.txt b/doc/manual.ja.txt
index dc6cd1b..1a9ca18 100644
--- a/doc/manual.ja.txt
+++ b/doc/manual.ja.txt
@@ -683,6 +683,10 @@ Tips
 
 クイックヘルプの行数を整数で指定します。
 
+### `ac-quick-help-prefer-pos-tip` ###
+
+auto-completeがクイックヘルプの表示にpos-tipによるネイティブのツールチップを使うかどうかです。non-nilなら追加で[pos-tip.el](http://www.emacswiki.org/emacs/PosTip)をインストールする必要があります。
+
 ### `ac-candidate-limit` ###
 
 補完候補数を制限します。整数が指定されている場合は、その値を表示する補完候補数の上限にします。`nil`の場合は無制限です。
diff --git a/doc/manual.txt b/doc/manual.txt
index 989ad40..dfe6d9e 100644
--- a/doc/manual.txt
+++ b/doc/manual.txt
@@ -679,6 +679,10 @@ Specify an integer of lines of completion menu.
 
 Specify an integer of lines of quick help.
 
+### `ac-quick-help-prefer-pos-tip` ###
+
+Whether or not auto-complete prefers native tooltip with pos-tip than overlap popup for displaying quick help. If non-nil, you also need to install [pos-tip.el](http://www.emacswiki.org/emacs/PosTip) so that displaying tooltip can work well.
+
 ### `ac-candidate-limit` ###
 
 Limit a number of candidates. Specifying an integer, the value will be a limit of candidates. `nil` means no limit.