diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index 225c6c9f2e5..7edf1ec4554 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -8,7 +8,7 @@ git-commit - Record changes to the repository
 SYNOPSIS
 --------
 [verse]
-'git commit' [-a | --interactive | --patch] [-s] [-v] [-u<mode>] [--amend]
+'git commit' [-a | --interactive | --patch] [-s[<mode>]] [-v] [-u<mode>] [--amend]
 	   [--dry-run] [(-c | -C | --squash) <commit> | --fixup [(amend|reword):]<commit>)]
 	   [-F <file> | -m <msg>] [--reset-author] [--allow-empty]
 	   [--allow-empty-message] [--no-verify] [-e] [--author=<author>]
diff --git a/Documentation/signoff-option.txt b/Documentation/signoff-option.txt
index 12aa2333e46..d8b06f1e791 100644
--- a/Documentation/signoff-option.txt
+++ b/Documentation/signoff-option.txt
@@ -1,7 +1,7 @@
 ifdef::git-commit[]
--s::
+-s[<mode>]::
 endif::git-commit[]
---signoff::
+--signoff[=<mode>]::
 --no-signoff::
 	Add a `Signed-off-by` trailer by the committer at the end of the commit
 	log message.  The meaning of a signoff depends on the project
@@ -16,3 +16,13 @@ endif::git-commit[]
 +
 The --no-signoff option can be used to countermand an earlier --signoff
 option on the command line.
++
+The mode parameter is optional (defaults to no-dedup), and is used to specify
+if it should deduplicate the `Signed-off-by` trailer or not when trying to
+add it to the trailers.
++
+The possible options are:
++
+	- 'no-dedup' - Will add the trailer unless it's already the last line.
+	- 'dedup' - Will not add the trailer if it's already anywhere in the
+	  trailers.
diff --git a/builtin/commit.c b/builtin/commit.c
index 06b1330346f..cd769af5bf0 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -40,7 +40,7 @@
 #include "pretty.h"
 
 static const char * const builtin_commit_usage[] = {
-	N_("git commit [-a | --interactive | --patch] [-s] [-v] [-u<mode>] [--amend]\n"
+	N_("git commit [-a | --interactive | --patch] [-s[<mode>]] [-v] [-u<mode>] [--amend]\n"
 	   "           [--dry-run] [(-c | -C | --squash) <commit> | --fixup [(amend|reword):]<commit>)]\n"
 	   "           [-F <file> | -m <msg>] [--reset-author] [--allow-empty]\n"
 	   "           [--allow-empty-message] [--no-verify] [-e] [--author=<author>]\n"
@@ -116,13 +116,13 @@ static const char *author_message, *author_message_buffer;
 static char *edit_message, *use_message;
 static char *fixup_message, *fixup_commit, *squash_message;
 static const char *fixup_prefix;
-static int all, also, interactive, patch_interactive, only, amend, signoff;
+static int all, also, interactive, patch_interactive, only, amend;
 static int edit_flag = -1; /* unspecified */
 static int quiet, verbose, no_verify, allow_empty, dry_run, renew_authorship;
 static int config_commit_verbose = -1; /* unspecified */
 static int no_post_rewrite, allow_empty_message, pathspec_file_nul;
 static char *untracked_files_arg, *force_date, *ignore_submodule_arg, *ignored_arg;
-static char *sign_commit, *pathspec_from_file;
+static char *sign_commit, *pathspec_from_file, *signoff_arg;
 static struct strvec trailer_args = STRVEC_INIT;
 
 /*
@@ -888,8 +888,14 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	if (clean_message_contents)
 		strbuf_stripspace(&sb, 0);
 
-	if (signoff)
-		append_signoff(&sb, ignore_non_trailer(sb.buf, sb.len), 0);
+	if (signoff_arg) {
+		if (!strcmp(signoff_arg, "dedup"))
+			append_signoff(&sb, ignore_non_trailer(sb.buf, sb.len), 1);
+		else if (!strcmp(signoff_arg, "no-dedup"))
+			append_signoff(&sb, ignore_non_trailer(sb.buf, sb.len), 0);
+		else
+			die(_("Invalid signoff mode: %s"), signoff_arg);
+	}
 
 	if (fwrite(sb.buf, 1, sb.len, s->fp) < sb.len)
 		die_errno(_("could not write commit template"));
@@ -1645,7 +1651,8 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "squash", &squash_message, N_("commit"), N_("use autosquash formatted message to squash specified commit")),
 		OPT_BOOL(0, "reset-author", &renew_authorship, N_("the commit is authored by me now (used with -C/-c/--amend)")),
 		OPT_CALLBACK_F(0, "trailer", &trailer_args, N_("trailer"), N_("add custom trailer(s)"), PARSE_OPT_NONEG, opt_pass_trailer),
-		OPT_BOOL('s', "signoff", &signoff, N_("add a Signed-off-by trailer")),
+		{ OPTION_STRING, 's', "signoff", &signoff_arg, N_("mode"),
+		  N_("add a Signed-off-by trailer, optional modes: no-dedup, dedup. (Default: no-dedup)"), PARSE_OPT_OPTARG, NULL, (intptr_t) "no-dedup" },
 		OPT_FILENAME('t', "template", &template_file, N_("use specified template file")),
 		OPT_BOOL('e', "edit", &edit_flag, N_("force edit of commit")),
 		OPT_CLEANUP(&cleanup_arg),
diff --git a/t/t7501-commit-basic-functionality.sh b/t/t7501-commit-basic-functionality.sh
index fb5417d5e7e..64e710879ab 100755
--- a/t/t7501-commit-basic-functionality.sh
+++ b/t/t7501-commit-basic-functionality.sh
@@ -541,6 +541,75 @@ test_expect_success 'signoff not confused by ---' '
 	test_cmp expected actual
 '
 
+test_expect_success 'signoff default mode adds when not last in trailers' '
+	cat >message <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+	EOF
+	cat >expected <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+	EOF
+	git commit --allow-empty --signoff -F message &&
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'signoff no-dedup mode adds when not last in trailers' '
+	cat >message <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+	EOF
+	cat >expected <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+	EOF
+	git commit --allow-empty --signoff=no-dedup -F message &&
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expected actual
+'
+
+
+test_expect_success 'signoff dedup mode does not duplicate when not last in trailers' '
+	cat >message <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+	EOF
+	cat >expected <<-EOF &&
+		subject
+
+		body
+
+		Signed-off-by: $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL>
+		Signed-off-by: A. U. <author@example.com>
+	EOF
+	git commit --allow-empty --signoff=dedup -F message &&
+	git log -1 --pretty=format:%B >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'multiple -m' '
 
 	>negative &&
