diff --git a/lisp/vc/vc-bzr.el b/lisp/vc/vc-bzr.el
index df8005309ce..fb7361120fb 100644
--- a/lisp/vc/vc-bzr.el
+++ b/lisp/vc/vc-bzr.el
@@ -822,13 +822,12 @@ If LIMIT is non-nil, show no more than this many entries."
 	 (list "--theirs-only" (and (not (string-empty-p upstream-location))
                                     upstream-location))))
 
-(defun vc-bzr-incoming-revision (upstream-location &optional _refresh)
+(defun vc-bzr-incoming-revision (&optional upstream-location _refresh)
   (with-temp-buffer
     (vc-bzr-command "missing" t 1 nil
                     "--log-format=long" "--show-ids"
                     "--theirs-only" "-r-1.."
-                    (and (not (string-empty-p upstream-location))
-		         upstream-location))
+                    upstream-location)
     (goto-char (point-min))
     (and (re-search-forward "^revision-id: " nil t)
          (buffer-substring (point) (pos-eol)))))
diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 1a4e10ea9f2..2524becafe4 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -70,7 +70,7 @@
 ;; - get-change-comment (files rev)                OK
 ;; HISTORY FUNCTIONS
 ;; * print-log (files buffer &optional shortlog start-revision limit)   OK
-;; * incoming-revision (upstream-location &optional refresh)   OK
+;; * incoming-revision (&optional upstream-location refresh)   OK
 ;; - log-search (buffer pattern)                   OK
 ;; - log-view-mode ()                              OK
 ;; - show-log-entry (revision)                     OK
@@ -1741,13 +1741,11 @@ If LIMIT is a non-empty string, use it as a base revision."
                               start-revision))
 		'("--")))))))
 
-(defun vc-git-incoming-revision (upstream-location &optional refresh)
-  (let ((rev (if (string-empty-p upstream-location)
-		 "@{upstream}"
-	       upstream-location)))
+(defun vc-git-incoming-revision (&optional upstream-location refresh)
+  (let ((rev (or upstream-location "@{upstream}")))
     (when (or refresh (null (vc-git--rev-parse rev)))
       (vc-git-command nil 0 nil "fetch"
-                      (and (not (string-empty-p upstream-location))
+                      (and upstream-location
                            ;; Extract remote from "remote/branch".
                            (replace-regexp-in-string "/.*" ""
                                                      upstream-location))))
diff --git a/lisp/vc/vc-hg.el b/lisp/vc/vc-hg.el
index fe977df6aae..4349e21ef7a 100644
--- a/lisp/vc/vc-hg.el
+++ b/lisp/vc/vc-hg.el
@@ -1549,10 +1549,8 @@ This runs the command \"hg summary\"."
          (nreverse result))
        "\n"))))
 
-(defun vc-hg-incoming-revision (upstream-location &optional _refresh)
-  (let* ((upstream-location (if (string-empty-p upstream-location)
-                              "default"
-                            upstream-location))
+(defun vc-hg-incoming-revision (&optional upstream-location _refresh)
+  (let* ((upstream-location (or upstream-location "default"))
          ;; Use 'hg identify' like this, and not 'hg incoming', because
          ;; this will give a sensible answer regardless of whether the
          ;; incoming revision has been pulled yet.
diff --git a/lisp/vc/vc.el b/lisp/vc/vc.el
index bc43239354e..d0c86ba1201 100644
--- a/lisp/vc/vc.el
+++ b/lisp/vc/vc.el
@@ -427,9 +427,10 @@
 ;;   received when performing a pull operation from UPSTREAM-LOCATION.
 ;;   Deprecated: implement incoming-revision and mergebase instead.
 ;;
-;; * incoming-revision (upstream-location &optional refresh)
+;; * incoming-revision (&optional upstream-location refresh)
 ;;
 ;;   Return revision at the head of the branch at UPSTREAM-LOCATION.
+;;   UPSTREAM-LOCATION defaults to where `vc-update' would pull from.
 ;;   If there is no such branch there, return nil.  (Should signal an
 ;;   error, not return nil, in the case that fetching data fails.)
 ;;   For a distributed VCS, should also fetch that revision into local
@@ -2752,8 +2753,7 @@ global binding."
   (let* ((fileset (or fileset (vc-deduce-fileset t)))
          (backend (car fileset))
          (incoming (vc--incoming-revision backend
-                                          (or upstream-location "")
-                                          'refresh)))
+                                          upstream-location 'refresh)))
     (vc-diff-internal vc-allow-async-diff fileset
                       (vc-call-backend backend 'mergebase incoming)
                       incoming
@@ -2799,8 +2799,7 @@ global binding."
   (interactive (list (vc--maybe-read-upstream-location)))
   (let* ((fileset (or fileset (vc-deduce-fileset t)))
          (backend (car fileset))
-         (incoming (vc--incoming-revision backend
-                                          (or upstream-location ""))))
+         (incoming (vc--incoming-revision backend upstream-location)))
     (vc-diff-internal vc-allow-async-diff fileset
                       (vc-call-backend backend 'mergebase incoming)
                       ;; FIXME: In order to exclude uncommitted
@@ -2885,8 +2884,7 @@ includes uncommitted changes."
   (interactive (list (vc--maybe-read-upstream-location) nil))
   (let* ((fileset (or fileset (vc-deduce-fileset t)))
          (backend (car fileset))
-         (incoming (vc--incoming-revision backend
-                                          (or upstream-location ""))))
+         (incoming (vc--incoming-revision backend upstream-location)))
     (vc-diff-internal vc-allow-async-diff fileset
                       (vc-call-backend backend 'mergebase incoming)
                       nil
@@ -3744,7 +3742,7 @@ The command prompts for the branch whose change log to show."
        (read-string "Upstream location/branch (empty for default): " nil
                     'vc-remote-location-history)))
 
-(defun vc--incoming-revision (backend upstream-location &optional refresh)
+(defun vc--incoming-revision (backend &optional upstream-location refresh)
   (or (vc-call-backend backend 'incoming-revision upstream-location refresh)
       (user-error "No incoming revision -- local-only branch?")))