diff --git a/m4/knot-code-coverage.m4 b/m4/knot-code-coverage.m4
index ae4f41694..430e1c455 100644
--- a/m4/knot-code-coverage.m4
+++ b/m4/knot-code-coverage.m4
@@ -1,16 +1,6 @@
-# Copyright 2014 CZ.NIC, z.s.p.o.
-#
-# This program is free software: you can redistribute it and/or modify it 
-# under the terms of the GNU General Public License version 3, as published 
-# by the Free Software Foundation.
-#
-# This program is distributed in the hope that it will be useful, but 
-# WITHOUT ANY WARRANTY; without even the implied warranties of 
-# MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR 
-# PURPOSE.  See the GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License along 
-# with this program.  If not, see <https://www.gnu.org/licenses/>.
+# Copyright (C) CZ.NIC, z.s.p.o. and contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+# For more information, see <https://www.knot-dns.cz/>
 
 AC_DEFUN([AX_CODE_COVERAGE], [
 	dnl Check for --enable-code-coverage
diff --git a/m4/knot-lib-version.m4 b/m4/knot-lib-version.m4
index 16279572f..7ce10641c 100644
--- a/m4/knot-lib-version.m4
+++ b/m4/knot-lib-version.m4
@@ -1,3 +1,7 @@
+# Copyright (C) CZ.NIC, z.s.p.o. and contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+# For more information, see <https://www.knot-dns.cz/>
+
 # KNOT_LIB_VERSION([library-name], [current], [revision], [age])
 # --------------------------------------------------------------
 # See https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
diff --git a/m4/knot-module.m4 b/m4/knot-module.m4
index 5893830cf..a28963a29 100644
--- a/m4/knot-module.m4
+++ b/m4/knot-module.m4
@@ -1,3 +1,7 @@
+# Copyright (C) CZ.NIC, z.s.p.o. and contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+# For more information, see <https://www.knot-dns.cz/>
+
 # KNOT_MODULE([module-name], [default], [non-shareable])
 # ------------------------------------------------------
 # Set Knot DNS module building
diff --git a/m4/knot-sanitizer.m4 b/m4/knot-sanitizer.m4
index 439d441be..19c804b7c 100644
--- a/m4/knot-sanitizer.m4
+++ b/m4/knot-sanitizer.m4
@@ -1,18 +1,7 @@
-# Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
-#
-# This program is free software: you can redistribute it and/or modify it
-# under the terms of the GNU General Public License version 3, as published
-# by the Free Software Foundation.
-#
-# This program is distributed in the hope that it will be useful, but
-# WITHOUT ANY WARRANTY; without even the implied warranties of
-# MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
-# PURPOSE.  See the GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License along
-# with this program.  If not, see <https://www.gnu.org/licenses/>.
+# Copyright (C) CZ.NIC, z.s.p.o. and contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+# For more information, see <https://www.knot-dns.cz/>
 
-#
 # Processes --with-sanitizer, --with-fuzzer, and --with-oss-fuzz flags, checks
 # if the options are supported by the compiler, and sets the following
 # variables accordingly:
@@ -20,7 +9,6 @@
 # - sanitizer_CFLAGS  -fsanitize=...
 # - fuzzer_CLAGS      -fsanitize=...
 # - fuzzer_LDLAGS     -fsanitize=...
-#
 
 AC_DEFUN([AX_SANITIZER], [
 
diff --git a/m4/knot-version.m4 b/m4/knot-version.m4
index 79b6ffa6a..32afc16c6 100644
--- a/m4/knot-version.m4
+++ b/m4/knot-version.m4
@@ -1,3 +1,7 @@
+# Copyright (C) CZ.NIC, z.s.p.o. and contributors
+# SPDX-License-Identifier: GPL-2.0-or-later
+# For more information, see <https://www.knot-dns.cz/>
+
 ################################################################################
 # Knot DNS versions are as follows
 #