diff --git a/t/t3428-rebase-signoff.sh b/t/t3428-rebase-signoff.sh
index 975b859..133e541 100755
--- a/t/t3428-rebase-signoff.sh
+++ b/t/t3428-rebase-signoff.sh
@@ -40,15 +40,13 @@
 # on the next subtest we can show that --no-signoff overrides the alias
 test_expect_success 'rebase --signoff adds a sign-off line' '
 	git rbs HEAD^ &&
-	git cat-file commit HEAD | sed -e "1,/^\$/d" > actual &&
-	test_cmp expected-signed actual
+	test_commit_message HEAD expected-signed
 '
 
 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_commit_message HEAD expected-unsigned
 '
 
 test_expect_success 'rebase --exec --signoff adds a sign-off line' '
@@ -56,30 +54,25 @@
 	git commit --amend -m "first" &&
 	git rebase --exec "touch exec" --signoff HEAD^ &&
 	test_path_is_file exec &&
-	git cat-file commit HEAD | sed -e "1,/^\$/d" >actual &&
-	test_cmp expected-signed actual
+	test_commit_message HEAD expected-signed
 '
 
 test_expect_success 'rebase --root --signoff adds a sign-off line' '
 	git commit --amend -m "first" &&
 	git rebase --root --keep-empty --signoff &&
-	git cat-file commit HEAD^ | sed -e "1,/^\$/d" >actual &&
-	test_cmp expected-initial-signed actual &&
-	git cat-file commit HEAD | sed -e "1,/^\$/d" >actual &&
-	test_cmp expected-signed actual
+	test_commit_message HEAD^ expected-initial-signed &&
+	test_commit_message HEAD expected-signed
 '
 
 test_expect_success 'rebase -i --signoff fails' '
 	git commit --amend -m "first" &&
 	git rebase -i --signoff HEAD^ &&
-	git cat-file commit HEAD | sed -e "1,/^\$/d" >actual &&
-	test_cmp expected-signed actual
+	test_commit_message HEAD expected-signed
 '
 
 test_expect_success 'rebase -m --signoff fails' '
 	git commit --amend -m "first" &&
 	git rebase -m --signoff HEAD^ &&
-	git cat-file commit HEAD | sed -e "1,/^\$/d" >actual &&
-	test_cmp expected-signed actual
+	test_commit_message HEAD expected-signed
 '
 test_done