diff --git a/exwm-input.el b/exwm-input.el
index 67e9a74..d581e7e 100644
--- a/exwm-input.el
+++ b/exwm-input.el
@@ -179,6 +179,7 @@ It's updated in several occasions, and only used by `exwm-input--set-focus'.")
 
 (declare-function exwm-floating--start-moveresize "exwm-floating.el"
                   (id &optional type))
+(declare-function exwm-workspace--position "exwm-workspace.el" (frame))
 
 (defvar exwm-workspace--list)
 
@@ -208,14 +209,14 @@ It's updated in several occasions, and only used by `exwm-input--set-focus'.")
                    (if (memq frame exwm-workspace--list)
                        ;; The X window is on another workspace
                        (exwm-workspace-switch
-                        (cl-position frame exwm-workspace--list))
+                        (exwm-workspace--position frame))
                      (with-current-buffer (window-buffer window)
                        (when (and (eq major-mode 'exwm-mode)
                                   (not (eq exwm--frame
                                            exwm-workspace--current)))
                          ;; The floating X window is on another workspace
                          (exwm-workspace-switch
-                          (cl-position exwm--frame exwm-workspace--list))))))
+                          (exwm-workspace--position exwm--frame))))))
                  ;; It has been reported that the `window' may have be deleted
                  (if (window-live-p window)
                      (select-window window)
diff --git a/exwm-layout.el b/exwm-layout.el
index 92ca677..db1aa0d 100644
--- a/exwm-layout.el
+++ b/exwm-layout.el
@@ -161,6 +161,7 @@
 (declare-function exwm-workspace--current-width  "exwm-workspace.el")
 (declare-function exwm-workspace--get-geometry "exwm-workspace.el" (frame))
 (declare-function exwm-workspace--minibuffer-own-frame-p "exwm-workspace.el")
+(declare-function exwm-workspace--position "exwm-workspace.el" (frame))
 (declare-function exwm-workspace--set-fullscreen "exwm-workspace.el" (frame))
 (declare-function exwm-workspace-move-window "exwm-workspace.el"
                   (index &optional id))
@@ -346,7 +347,7 @@ selected by `other-buffer'."
                 (if (eq frame exwm--frame)
                     (exwm-layout--show exwm--id window)
                   (exwm-workspace-move-window
-                   (cl-position frame exwm-workspace--list) exwm--id))
+                   (exwm-workspace--position frame) exwm--id))
                 ;; Make sure this buffer is not displayed elsewhere.  Note down
                 ;; windows displaying an EXWM-buffer now displayed elsewhere; we
                 ;; need to display with some other buffer there.
diff --git a/exwm-workspace.el b/exwm-workspace.el
index b2138aa..641f3f2 100644
--- a/exwm-workspace.el
+++ b/exwm-workspace.el
@@ -29,6 +29,13 @@
 
 (defvar exwm-workspace-number 4 "Number of workspaces (1 ~ 10).")
 (defvar exwm-workspace--list nil "List of all workspaces (Emacs frames).")
+
+(defsubst exwm-workspace--position (frame)
+  "Retrieve index of given FRAME in workspace list.
+
+NIL if FRAME is not a workspace"
+  (cl-position frame exwm-workspace--list))
+
 (defvar exwm-workspace--switch-map
   (let ((map (make-sparse-keymap)))
     (define-key map [t] (lambda () (interactive)))
@@ -72,7 +79,7 @@
         (with-current-buffer (cdr i)
           (when exwm--frame
             (setf (aref not-empty
-                        (cl-position exwm--frame exwm-workspace--list))
+                        (exwm-workspace--position exwm--frame))
                   t))))
       (setq exwm-workspace--switch-history
             (mapcar
@@ -948,13 +955,13 @@ applied to all subsequently created X frames."
                           :window workspace
                           :data
                           (format "EXWM workspace %d"
-                                  (cl-position i exwm-workspace--list))))
+                                  (exwm-workspace--position i))))
        (xcb:+request exwm--connection
            (make-instance 'xcb:ewmh:set-_NET_WM_NAME
                           :window container
                           :data
                           (format "EXWM workspace %d frame container"
-                                  (cl-position i exwm-workspace--list)))))
+                                  (exwm-workspace--position i)))))
       (xcb:+request exwm--connection
           (make-instance 'xcb:ReparentWindow
                          :window outer-id :parent container :x 0 :y 0))
diff --git a/exwm.el b/exwm.el
index 814104a..4a6e9fd 100644
--- a/exwm.el
+++ b/exwm.el
@@ -438,7 +438,7 @@
             ;; FIXME: check (may require other properties set)
             (when (memq xcb:Atom:_NET_WM_STATE_DEMANDS_ATTENTION props)
               (when (= action xcb:ewmh:_NET_WM_STATE_ADD)
-                (let ((idx (cl-position exwm--frame exwm-workspace--list)))
+                (let ((idx (exwm-workspace--position exwm--frame)))
                   (unless (= idx exwm-workspace-current-index)
                     (set-frame-parameter exwm--frame 'exwm--urgency t)
                     (setq exwm-workspace--switch-history-outdated t))))