diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 67d48e6883..53f4e14444 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -370,6 +370,11 @@ default is `--no-fork-point`, otherwise the default is `--fork-point`.
 	of the rebased commits (see linkgit:git-am[1]).
 	Incompatible with the --interactive option.
 
+--signoff::
+	This flag is passed to 'git am' to sign off all the rebased
+	commits (see linkgit:git-am[1]). Incompatible with the
+	--interactive option.
+
 -i::
 --interactive::
 	Make a list of the commits which are about to be rebased.  Let the
diff --git a/builtin/am.c b/builtin/am.c
index 805f56cec2..f08b7e6626 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1185,42 +1185,39 @@ static void NORETURN die_user_resolve(const struct am_state *state)
 	exit(128);
 }
 
-static void am_signoff(struct strbuf *sb)
-{
-	char *cp;
-	struct strbuf mine = STRBUF_INIT;
-
-	/* Does it end with our own sign-off? */
-	strbuf_addf(&mine, "\n%s%s\n",
-		    sign_off_header,
-		    fmt_name(getenv("GIT_COMMITTER_NAME"),
-			     getenv("GIT_COMMITTER_EMAIL")));
-	if (mine.len < sb->len &&
-	    !strcmp(mine.buf, sb->buf + sb->len - mine.len))
-		goto exit; /* no need to duplicate */
-
-	/* Does it have any Signed-off-by: in the text */
-	for (cp = sb->buf;
-	     cp && *cp && (cp = strstr(cp, sign_off_header)) != NULL;
-	     cp = strchr(cp, '\n')) {
-		if (sb->buf == cp || cp[-1] == '\n')
-			break;
-	}
-
-	strbuf_addstr(sb, mine.buf + !!cp);
-exit:
-	strbuf_release(&mine);
-}
-
 /**
  * Appends signoff to the "msg" field of the am_state.
  */
 static void am_append_signoff(struct am_state *state)
 {
+	char *cp;
+	struct strbuf mine = STRBUF_INIT;
 	struct strbuf sb = STRBUF_INIT;
 
 	strbuf_attach(&sb, state->msg, state->msg_len, state->msg_len);
-	am_signoff(&sb);
+
+	/* our sign-off */
+	strbuf_addf(&mine, "\n%s%s\n",
+		    sign_off_header,
+		    fmt_name(getenv("GIT_COMMITTER_NAME"),
+			     getenv("GIT_COMMITTER_EMAIL")));
+
+	/* Does sb end with it already? */
+	if (mine.len < sb.len &&
+	    !strcmp(mine.buf, sb.buf + sb.len - mine.len))
+		goto exit; /* no need to duplicate */
+
+	/* Does it have any Signed-off-by: in the text */
+	for (cp = sb.buf;
+	     cp && *cp && (cp = strstr(cp, sign_off_header)) != NULL;
+	     cp = strchr(cp, '\n')) {
+		if (sb.buf == cp || cp[-1] == '\n')
+			break;
+	}
+
+	strbuf_addstr(&sb, mine.buf + !!cp);
+exit:
+	strbuf_release(&mine);
 	state->msg = strbuf_detach(&sb, &state->msg_len);
 }
 
@@ -1325,9 +1322,6 @@ static int parse_mail(struct am_state *state, const char *mail)
 	strbuf_addbuf(&msg, &mi.log_message);
 	strbuf_stripspace(&msg, 0);
 
-	if (state->signoff)
-		am_signoff(&msg);
-
 	assert(!state->author_name);
 	state->author_name = strbuf_detach(&author_name, NULL);
 
@@ -1852,6 +1846,9 @@ static void am_run(struct am_state *state, int resume)
 			if (skip)
 				goto next; /* mail should be skipped */
 
+			if (state->signoff)
+				am_append_signoff(state);
+
 			write_author_script(state);
 			write_commit_msg(state);
 		}
diff --git a/git-rebase.sh b/git-rebase.sh
index 48d7c5ded4..db1deed846 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -34,6 +34,7 @@ root!              rebase all reachable commits up to the root(s)
 autosquash         move commits that begin with squash!/fixup! under -i
 committer-date-is-author-date! passed to 'git am'
 ignore-date!       passed to 'git am'
+signoff            passed to 'git am'
 whitespace=!       passed to 'git apply'
 ignore-whitespace! passed to 'git apply'
 C=!                passed to 'git apply'
@@ -321,7 +322,7 @@ do
 	--ignore-whitespace)
 		git_am_opt="$git_am_opt $1"
 		;;
-	--committer-date-is-author-date|--ignore-date)
+	--committer-date-is-author-date|--ignore-date|--signoff|--no-signoff)
 		git_am_opt="$git_am_opt $1"
 		force_rebase=t
 		;;
diff --git a/t/t3428-rebase-signoff.sh b/t/t3428-rebase-signoff.sh
new file mode 100755
index 0000000000..2afb564701
--- /dev/null
+++ b/t/t3428-rebase-signoff.sh
@@ -0,0 +1,46 @@
+#!/bin/sh
+
+test_description='git rebase --signoff
+
+This test runs git rebase --signoff and make sure that it works.
+'
+
+. ./test-lib.sh
+
+# A simple file to commit
+cat >file <<EOF
+a
+EOF
+
+# Expected commit message after rebase --signoff
+cat >expected-signed <<EOF
+first
+
+Signed-off-by: $(git var GIT_COMMITTER_IDENT | sed -e "s/>.*/>/")
+EOF
+
+# Expected commit message after rebase without --signoff (or with --no-signoff)
+cat >expected-unsigned <<EOF
+first
+EOF
+
+
+# We configure an alias to do the rebase --signoff so that
+# on the next subtest we can show that --no-signoff overrides the alias
+test_expect_success 'rebase --signoff adds a sign-off line' '
+	git commit --allow-empty -m "Initial empty commit" &&
+	git add file && git commit -m first &&
+	git config alias.rbs "rebase --signoff" &&
+	git rbs HEAD^ &&
+	git cat-file commit HEAD | sed -e "1,/^\$/d" > actual &&
+	test_cmp expected-signed actual
+'
+
+test_expect_success 'rebase --no-signoff does not add a sign-off line' '
+	git commit --amend -m "first" &&
+	git rbs --no-signoff HEAD^ &&
+	git cat-file commit HEAD | sed -e "1,/^\$/d" > actual &&
+	test_cmp expected-unsigned actual
+'
+
+test_done