2 files changed, 21 insertions, 0 deletions

diff --git a/lisp/replace.el b/lisp/replace.el
index 6cee2253746..d1eabb035d3 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -2576,6 +2576,7 @@ It must return a string."
                            (let ((stack-idx         0)
                                  (stack-len         (length stack))
                                  (num-replacements  0)
+                                 (nocasify t) ; Undo must preserve case (Bug#31073).
                                  search-string
                                  next-replacement)
                              (while (and (< stack-idx stack-len)
diff --git a/test/lisp/replace-tests.el b/test/lisp/replace-tests.el
index 66c68426607..40a1a31cf7c 100644
--- a/test/lisp/replace-tests.el
+++ b/test/lisp/replace-tests.el
@@ -380,4 +380,24 @@ Each element has the format:
   (should (string= "211" (replace-tests--query-replace-undo)))
   (should (string= "211" (replace-tests--query-replace-undo 'comma))))
 
+(ert-deftest query-replace-undo-bug31073 ()
+  "Test for https://debbugs.gnu.org/31073 ."
+  (let ((text "aaa aaa")
+        (count 0))
+    (with-temp-buffer
+      (insert text)
+      (goto-char 1)
+      (cl-letf (((symbol-function 'read-event)
+                 (lambda (&rest args)
+                   (cl-incf count)
+                   (let ((val (pcase count
+                                ((or 1 2 3) ?\s) ; replace current and go next
+                                (4 ?U) ; undo-all
+                                (_ ?q)))) ; exit
+                     val))))
+        (perform-replace "a" "B" t nil nil))
+      ;; After undo text must be the same.
+      (should (string= text (buffer-string))))))
+
+
 ;;; replace-tests.el ends here