 
 (defun git-update-index (index-file files)
   "Run git-update-index on a list of files."
-  (let ((env (and index-file `(("GIT_INDEX_FILE" . ,index-file))))
+  (let ((process-environment (append (and index-file (list (concat "GIT_INDEX_FILE=" index-file)))
+                                     process-environment))
         added deleted modified)
     (dolist (info files)
       (case (git-fileinfo->state info)
         ('added (push info added))
         ('deleted (push info deleted))
         ('modified (push info modified))))
-    (when added
-      (apply #'git-call-process-env nil env "update-index" "--add" "--" (git-get-filenames added)))
-    (when deleted
-      (apply #'git-call-process-env nil env "update-index" "--remove" "--" (git-get-filenames deleted)))
-    (when modified
-      (apply #'git-call-process-env nil env "update-index" "--" (git-get-filenames modified)))))
+    (and
+     (or (not added) (apply #'git-call-process-display-error "update-index" "--add" "--" (git-get-filenames added)))
+     (or (not deleted) (apply #'git-call-process-display-error "update-index" "--remove" "--" (git-get-filenames deleted)))
+     (or (not modified) (apply #'git-call-process-display-error "update-index" "--" (git-get-filenames modified))))))
 
 (defun git-run-pre-commit-hook ()
   "Run the pre-commit hook if any."

    (and (eq 0 (apply #' git-call-process-env t env args))
         (buffer-string))))

(defun git-run-process-region (buffer start end program args)
  "Run a git process with a buffer region as input."
  (let ((output-buffer (current-buffer))

          (message "You cannot commit unmerged files, resolve them first.")
        (unwind-protect
            (let ((files (git-marked-files-state 'added 'deleted 'modified))
                  head tree head-tree)
              (unless (git-empty-db-p)
                (setq head (git-rev-parse "HEAD")
                      head-tree (git-rev-parse "HEAD^{tree}")))
              (if files
                  (progn
                    (message "Running git commit...")
                    (when
                        (and
                         (git-read-tree head-tree index-file)
                         (git-update-index nil files)         ;update both the default index
                         (git-update-index index-file files)  ;and the temporary one
                         (setq tree (git-write-tree index-file)))
                      (if (or (not (string-equal tree head-tree))
                              (yes-or-no-p "The tree was not modified, do you really want to perform an empty commit? "))
                          (let ((commit (git-commit-tree buffer tree head)))
