diff --git a/autogen.sh b/autogen.sh
index d0f60dc68af..cff4a54be56 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -339,7 +339,7 @@ git_config diff.texinfo.xfuncname \
 tailored_hooks=
 sample_hooks=
 
-for hook in commit-msg pre-commit; do
+for hook in commit-msg pre-commit prepare-commit-msg; do
     cmp -- build-aux/git-hooks/$hook "$hooks/$hook" >/dev/null 2>&1 ||
 	tailored_hooks="$tailored_hooks $hook"
 done
diff --git a/build-aux/git-hooks/prepare-commit-msg b/build-aux/git-hooks/prepare-commit-msg
new file mode 100755
index 00000000000..3562a802234
--- /dev/null
+++ b/build-aux/git-hooks/prepare-commit-msg
@@ -0,0 +1,45 @@
+#!/bin/sh
+# Check the format of GNU Emacs change log entries.
+
+# Copyright 2019 Free Software Foundation, Inc.
+
+# This file is part of GNU Emacs.
+
+# GNU Emacs is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# GNU Emacs is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY 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 GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+COMMIT_MSG_FILE=$1
+COMMIT_SOURCE=$2
+SHA1=$3
+
+# Prefer gawk if available, as it handles NUL bytes properly.
+if type gawk >/dev/null 2>&1; then
+  awk=gawk
+else
+  awk=awk
+fi
+
+exec $awk '
+  # Catch the case when someone ran git-commit with -s option,
+  # which automatically adds Signed-off-by.
+  /^Signed-off-by: / {
+    print "'\''Signed-off-by:'\'' in commit message"
+    status = 1
+  }
+  END {
+    if (status != 0) {
+      print "Commit aborted; please see the file 'CONTRIBUTE'"
+    }
+    exit status
+  }
+' <"$COMMIT_MSG_FILE"
diff --git a/src/fns.c b/src/fns.c
index c3202495daf..6b1f7331f55 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -1131,10 +1131,8 @@ string the same way whether it is unibyte or multibyte.)  */)
 DEFUN ("string-make-unibyte", Fstring_make_unibyte, Sstring_make_unibyte,
        1, 1, 0,
        doc: /* Return the unibyte equivalent of STRING.
-Multibyte character codes are converted to unibyte according to
-`nonascii-translation-table' or, if that is nil, `nonascii-insert-offset'.
-If the lookup in the translation table fails, this function takes just
-the low 8 bits of each character.  */)
+Multibyte character codes above 255 are converted to unibyte
+by taking just the low 8 bits of each character's code.  */)
   (Lisp_Object string)
 {
   CHECK_STRING (string);
diff --git a/src/search.c b/src/search.c
index dfbae5c9628..8a0f707b723 100644
--- a/src/search.c
+++ b/src/search.c
@@ -1324,12 +1324,7 @@ search_buffer_non_re (Lisp_Object string, ptrdiff_t pos,
     }
   else
     {
-      /* Converting multibyte to single-byte.
-
-         ??? Perhaps this conversion should be done in a special way
-         by subtracting nonascii-insert-offset from each non-ASCII char,
-         so that only the multibyte chars which really correspond to
-         the chosen single-byte character set can possibly match.  */
+      /* Converting multibyte to single-byte.  */
       raw_pattern_size = SCHARS (string);
       raw_pattern_size_byte = SCHARS (string);
       raw_pattern = SAFE_ALLOCA (raw_pattern_size + 1);