diff --git a/.editorconfig b/.editorconfig
index 2d3929b591..6e4eaa8e95 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -4,7 +4,7 @@ insert_final_newline = true
 
 # The settings for C (*.c and *.h) files are mirrored in .clang-format.  Keep
 # them in sync.
-[{*.{c,h,sh,bash,perl,pl,pm,txt,adoc},config.mak.*,Makefile}]
+[{*.{c,h,sh,bash,perl,pl,pm,txt,adoc},config.mak.*,Makefile,templates/hooks/*.sample}]
 indent_style = tab
 tab_width = 8
 
diff --git a/.gitattributes b/.gitattributes
index 38b1c52fe0..556322be01 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -18,3 +18,4 @@ CODE_OF_CONDUCT.md -whitespace
 /Documentation/user-manual.adoc conflict-marker-size=32
 /t/t????-*.sh conflict-marker-size=32
 /t/unit-tests/clar/test/expected/* whitespace=-blank-at-eof
+/templates/hooks/*.sample whitespace=indent,trail,space,incomplete text eol=lf
diff --git a/templates/hooks/commit-msg.sample b/templates/hooks/commit-msg.sample
index b58d1184a9..f7458efe62 100755
--- a/templates/hooks/commit-msg.sample
+++ b/templates/hooks/commit-msg.sample
@@ -15,10 +15,60 @@
 # SOB=$(git var GIT_AUTHOR_IDENT | sed -n 's/^\(.*>\).*$/Signed-off-by: \1/p')
 # grep -qs "^$SOB" "$1" || echo "$SOB" >> "$1"
 
-# This example catches duplicate Signed-off-by lines.
+# This example catches duplicate Signed-off-by lines and messages that
+# would confuse 'git am'.
+
+ret=0
 
 test "" = "$(grep '^Signed-off-by: ' "$1" |
 	 sort | uniq -c | sed -e '/^[ 	]*1[ 	]/d')" || {
 	echo >&2 Duplicate Signed-off-by lines.
-	exit 1
+	ret=1
 }
+
+comment_re="$(
+	{
+		git config --get-regexp "^core\.comment(char|string)\$" ||
+			echo '#'
+	} | sed -n -e '
+		${
+			s/^[^ ]* //
+			s|[][*./\]|\\&|g
+			s/^auto$/[#;@!$%^&|:]/
+			p
+		}'
+)"
+scissors_line="^${comment_re} -\{8,\} >8 -\{8,\}\$"
+comment_line="^${comment_re}.*"
+blank_line='^[ 	]*$'
+# Disallow lines starting with "diff -" or "Index: " in the body of the
+# message. Stop looking if we see a scissors line.
+line="$(sed -n -e "
+	# Skip comments and blank lines at the start of the file.
+	/${scissors_line}/q
+	/${comment_line}/d
+	/${blank_line}/d
+	# The first paragraph will become the subject header so
+	# does not need to be checked.
+	: subject
+	n
+	/${scissors_line}/q
+	/${blank_line}/!b subject
+	# Check the body of the message for problematic
+	# prefixes.
+	: body
+	n
+	/${scissors_line}/q
+	/${comment_line}/b body
+	/^diff -/{p;q;}
+	/^Index: /{p;q;}
+	b body
+	" "$1")"
+if test -n "$line"
+then
+	echo >&2 "Message contains a diff that will confuse 'git am'."
+	echo >&2 "To fix this indent the diff."
+	ret=1
+fi
+
+exit $ret