1 files changed, 23 insertions, 9 deletions

diff --git a/lisp/files.el b/lisp/files.el
index b57e35b9a0a..6a68c631549 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2909,11 +2909,18 @@ we don't actually set it to the same mode the buffer already has."
                          (narrow-to-region (point-min)
                                            (min (point-max)
                                                 (+ (point-min) magic-mode-regexp-match-limit)))
-                         (assoc-default nil magic-mode-alist
-                                        (lambda (re _dummy)
-                                          (if (functionp re)
-                                              (funcall re)
-                                            (looking-at re)))))))
+                         (assoc-default
+                          nil magic-mode-alist
+                          (lambda (re _dummy)
+                            (cond
+                             ((functionp re)
+                              (funcall re))
+                             ((stringp re)
+                              (looking-at re))
+                             (t
+                              (error
+                               "Problem in magic-mode-alist with element %s"
+                               re))))))))
           (set-auto-mode-0 done keep-mode-if-same)))
     ;; Next compare the filename against the entries in auto-mode-alist.
     (unless done
@@ -2965,10 +2972,17 @@ we don't actually set it to the same mode the buffer already has."
                                            (min (point-max)
                                                 (+ (point-min) magic-mode-regexp-match-limit)))
                          (assoc-default nil magic-fallback-mode-alist
-                                        (lambda (re _dummy)
-                                          (if (functionp re)
-                                              (funcall re)
-                                            (looking-at re)))))))
+                                        (lambda (re _dummy)
+                                          (cond
+                                           ((functionp re)
+                                            (funcall re))
+                                           ((stringp re)
+                                            (looking-at re))
+                                           (t
+                                            (error
+                                             "Problem with magic-fallback-mode-alist element: %s"
+                                             re))
+                                           ))))))
           (set-auto-mode-0 done keep-mode-if-same)))
     (unless done
       (set-buffer-major-mode (current-buffer)))))