diff --git a/build-aux/GNUmakefile.in b/build-aux/GNUmakefile.in
index a4c39601..5610e006 100644
--- a/build-aux/GNUmakefile.in
+++ b/build-aux/GNUmakefile.in
@@ -1,5 +1,5 @@
 # GNU Mes --- Maxwell Equations of Software
-# Copyright © 2018,2019,2021 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+# Copyright © 2018,2019,2021,2022 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
 #
 # This file is part of GNU Mes.
 #
@@ -337,9 +337,9 @@ tag:
 #  2. Create signed tarball
 #     make sign-dist
 #  3. Update Guix package description
-#     - make release
+#     make release
 #  4. Finish announcement
-#     - Update doc/announce/ANNOUNCE-0.23
+#     - make sum-announce
 #     - doc: Post-release update.
 #     - build-aux/GNUMakefile.in: gen-announce: update previous-version
 #  5. Verify
@@ -377,6 +377,13 @@ gen-announce:
 	    --news=NEWS\
             > doc/announce/ANNOUNCE-$(VERSION)
 
+sum-announce:
+	sed -i																				\
+	    -e "s,  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  $(PACKAGE)-$(VERSION).tar.gz,  $(shell sha256sum $(PACKAGE)-$(VERSION).tar.gz),"	\
+	    -e "s,  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  $(PACKAGE)-$(VERSION).tar.gz,  $(shell sha1sum $(PACKAGE)-$(VERSION).tar.gz),"				\
+	    -e "s,  xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx  $(PACKAGE)-$(VERSION).tar.gz,  $(shell md5sum $(PACKAGE)-$(VERSION).tar.gz),"					\
+	doc/announce/ANNOUNCE-$(VERSION)
+
 installdirs: mkinstalldirs
 	mkdir -p\
 	    $(DESTDIR)$(bindir)\