Index: tools/clang-format/clang-format.el
===================================================================
--- tools/clang-format/clang-format.el
+++ tools/clang-format/clang-format.el
@@ -147,16 +147,15 @@
         ;; always use ‘utf-8-unix’ and ignore the buffer coding system.
         (default-process-coding-system '(utf-8-unix . utf-8-unix)))
     (unwind-protect
-        (let ((status (apply 'call-process-region
-                             (append `(nil nil ,clang-format-executable
-                                           nil (,temp-buffer ,temp-file) nil)
-                                     '("-output-replacements-xml")
-                                     (if assume-file
-                                         `("-assume-filename" ,assume-file) nil)
-                                     `("-style" ,style
-                                       "-offset" ,(number-to-string file-start)
-                                       "-length" ,(number-to-string (- file-end file-start))
-                                       "-cursor" ,(number-to-string cursor)))))
+        (let ((status (apply #'call-process-region
+                             nil nil clang-format-executable
+                             nil `(,temp-buffer ,temp-file) nil
+                             `("-output-replacements-xml"
+                               ,@(and assume-file (list "-assume-filename" assume-file))
+                               "-style" ,style
+                               "-offset" ,(number-to-string file-start)
+                               "-length" ,(number-to-string (- file-end file-start))
+                               "-cursor" ,(number-to-string cursor))))
               (stderr (with-temp-buffer
                         (unless (zerop (cadr (insert-file-contents temp-file)))
                           (insert ": "))