diff --git a/t/t3415-rebase-autosquash.sh b/t/t3415-rebase-autosquash.sh
index b77a413b1c9..0028533e0bf 100755
--- a/t/t3415-rebase-autosquash.sh
+++ b/t/t3415-rebase-autosquash.sh
@@ -115,4 +115,8 @@ test_expect_success 'use commit --fixup' '
 	test_auto_commit_flags fixup 1
 '
 
+test_expect_success 'use commit --squash' '
+	test_auto_commit_flags squash 2
+'
+
 test_done
diff --git a/t/t3900-i18n-commit.sh b/t/t3900-i18n-commit.sh
index f4775ee2856..c06a5ee7660 100755
--- a/t/t3900-i18n-commit.sh
+++ b/t/t3900-i18n-commit.sh
@@ -160,4 +160,6 @@ test_commit_autosquash_flags () {
 
 test_commit_autosquash_flags eucJP fixup
 
+test_commit_autosquash_flags ISO-2022-JP squash '-m "squash message"'
+
 test_done
diff --git a/t/t7500-commit.sh b/t/t7500-commit.sh
index a41b819f6c9..162527c2114 100755
--- a/t/t7500-commit.sh
+++ b/t/t7500-commit.sh
@@ -238,10 +238,57 @@ test_expect_success 'commit --fixup provides correct one-line commit message' '
 	commit_msg_is "fixup! target message subject line"
 '
 
+test_expect_success 'commit --squash works with -F' '
+	commit_for_rebase_autosquash_setup &&
+	echo "log message from file" >msgfile &&
+	git commit --squash HEAD~1 -F msgfile  &&
+	commit_msg_is "squash! target message subject linelog message from file"
+'
+
+test_expect_success 'commit --squash works with -m' '
+	commit_for_rebase_autosquash_setup &&
+	git commit --squash HEAD~1 -m "foo bar\nbaz" &&
+	commit_msg_is "squash! target message subject linefoo bar\nbaz"
+'
+
+test_expect_success 'commit --squash works with -C' '
+	commit_for_rebase_autosquash_setup &&
+	git commit --squash HEAD~1 -C HEAD &&
+	commit_msg_is "squash! target message subject lineintermediate commit"
+'
+
+test_expect_success 'commit --squash works with -c' '
+	commit_for_rebase_autosquash_setup &&
+	test_set_editor "$TEST_DIRECTORY"/t7500/edit-content &&
+	git commit --squash HEAD~1 -c HEAD &&
+	commit_msg_is "squash! target message subject lineedited commit"
+'
+
+test_expect_success 'commit --squash works with -C for same commit' '
+	commit_for_rebase_autosquash_setup &&
+	git commit --squash HEAD -C HEAD &&
+	commit_msg_is "squash! intermediate commit"
+'
+
+test_expect_success 'commit --squash works with -c for same commit' '
+	commit_for_rebase_autosquash_setup &&
+	test_set_editor "$TEST_DIRECTORY"/t7500/edit-content &&
+	git commit --squash HEAD -c HEAD &&
+	commit_msg_is "squash! edited commit"
+'
+
+test_expect_success 'commit --squash works with editor' '
+	commit_for_rebase_autosquash_setup &&
+	test_set_editor "$TEST_DIRECTORY"/t7500/add-content &&
+	git commit --squash HEAD~1 &&
+	commit_msg_is "squash! target message subject linecommit message"
+'
+
 test_expect_success 'invalid message options when using --fixup' '
 	echo changes >>foo &&
 	echo "message" >log &&
 	git add foo &&
+	test_must_fail git commit --fixup HEAD~1 --squash HEAD~2 &&
 	test_must_fail git commit --fixup HEAD~1 -C HEAD~2 &&
 	test_must_fail git commit --fixup HEAD~1 -c HEAD~2 &&
 	test_must_fail git commit --fixup HEAD~1 -m "cmdline message" &&
diff --git a/t/t7500/edit-content b/t/t7500/edit-content
new file mode 100755
index 00000000000..08db9fdd2e6
--- /dev/null
+++ b/t/t7500/edit-content
@@ -0,0 +1,4 @@
+#!/bin/sh
+sed -e "s/intermediate/edited/g" <"$1" >"$1-"
+mv "$1-" "$1"
+exit 0