diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
index 9e4d9a0619..b06782bc79 100755
--- a/contrib/subtree/git-subtree.sh
+++ b/contrib/subtree/git-subtree.sh
@@ -44,17 +44,6 @@ squash        merge subtree changes as a single commit
 m,message=    use the given message as the commit message for the merge commit
 "
 
-arg_debug=
-arg_command=
-arg_prefix=
-arg_split_branch=
-arg_split_onto=
-arg_split_rejoin=
-arg_split_ignore_joins=
-arg_split_annotate=
-arg_addmerge_squash=
-arg_addmerge_message=
-
 indent=0
 
 # Usage: debug [MSG...]
@@ -106,10 +95,61 @@ main () {
 	then
 		set -- -h
 	fi
-	eval "$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
+	set_args="$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
+	eval "$set_args"
 	. git-sh-setup
 	require_work_tree
 
+	# First figure out the command and whether we use --rejoin, so
+	# that we can provide more helpful validation when we do the
+	# "real" flag parsing.
+	arg_split_rejoin=
+	allow_split=
+	allow_addmerge=
+	while test $# -gt 0
+	do
+		opt="$1"
+		shift
+		case "$opt" in
+			--annotate|-b|-P|-m|--onto)
+				shift
+				;;
+			--rejoin)
+				arg_split_rejoin=1
+				;;
+			--no-rejoin)
+				arg_split_rejoin=
+				;;
+			--)
+				break
+				;;
+		esac
+	done
+	arg_command=$1
+	case "$arg_command" in
+	add|merge|pull)
+		allow_addmerge=1
+		;;
+	split|push)
+		allow_split=1
+		allow_addmerge=$arg_split_rejoin
+		;;
+	*)
+		die "Unknown command '$arg_command'"
+		;;
+	esac
+	# Reset the arguments array for "real" flag parsing.
+	eval "$set_args"
+
+	# Begin "real" flag parsing.
+	arg_debug=
+	arg_prefix=
+	arg_split_branch=
+	arg_split_onto=
+	arg_split_ignore_joins=
+	arg_split_annotate=
+	arg_addmerge_squash=
+	arg_addmerge_message=
 	while test $# -gt 0
 	do
 		opt="$1"
@@ -123,13 +163,16 @@ main () {
 			arg_debug=1
 			;;
 		--annotate)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_annotate="$1"
 			shift
 			;;
 		--no-annotate)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_annotate=
 			;;
 		-b)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_branch="$1"
 			shift
 			;;
@@ -138,6 +181,7 @@ main () {
 			shift
 			;;
 		-m)
+			test -n "$allow_addmerge" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_addmerge_message="$1"
 			shift
 			;;
@@ -145,28 +189,34 @@ main () {
 			arg_prefix=
 			;;
 		--onto)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_onto="$1"
 			shift
 			;;
 		--no-onto)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_onto=
 			;;
 		--rejoin)
-			arg_split_rejoin=1
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			;;
 		--no-rejoin)
-			arg_split_rejoin=
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			;;
 		--ignore-joins)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_ignore_joins=1
 			;;
 		--no-ignore-joins)
+			test -n "$allow_split" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_split_ignore_joins=
 			;;
 		--squash)
+			test -n "$allow_addmerge" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_addmerge_squash=1
 			;;
 		--no-squash)
+			test -n "$allow_addmerge" || die "The '$opt' flag does not make sense with 'git subtree $arg_command'."
 			arg_addmerge_squash=
 			;;
 		--)
@@ -177,19 +227,8 @@ main () {
 			;;
 		esac
 	done
-
-	arg_command="$1"
 	shift
 
-	case "$arg_command" in
-	add|merge|pull|split|push)
-		:
-		;;
-	*)
-		die "Unknown command '$arg_command'"
-		;;
-	esac
-
 	if test -z "$arg_prefix"
 	then
 		die "You must provide the --prefix option."
diff --git a/contrib/subtree/t/t7900-subtree.sh b/contrib/subtree/t/t7900-subtree.sh
index d7ad6ffff0..4153b65321 100755
--- a/contrib/subtree/t/t7900-subtree.sh
+++ b/contrib/subtree/t/t7900-subtree.sh
@@ -33,6 +33,12 @@ test_create_commit () (
 	git commit -m "$commit" || error "Could not commit"
 )
 
+test_wrong_flag() {
+	test_must_fail "$@" >out 2>err &&
+	test_must_be_empty out &&
+	grep "flag does not make sense with" err
+}
+
 last_commit_subject () {
 	git log --pretty=format:%s -1
 }
@@ -72,6 +78,22 @@ test_expect_success 'no pull from non-existent subtree' '
 	)
 '
 
+test_expect_success 'add rejects flags for split' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		test_wrong_flag git subtree add --prefix="sub dir" --annotate=foo FETCH_HEAD &&
+		test_wrong_flag git subtree add --prefix="sub dir" --branch=foo FETCH_HEAD &&
+		test_wrong_flag git subtree add --prefix="sub dir" --ignore-joins FETCH_HEAD &&
+		test_wrong_flag git subtree add --prefix="sub dir" --onto=foo FETCH_HEAD &&
+		test_wrong_flag git subtree add --prefix="sub dir" --rejoin FETCH_HEAD
+	)
+'
+
 test_expect_success 'add subproj as subtree into sub dir/ with --prefix' '
 	subtree_test_create_repo "$test_count" &&
 	subtree_test_create_repo "$test_count/sub proj" &&
@@ -128,6 +150,28 @@ test_expect_success 'add subproj as subtree into sub dir/ with --squash and --pr
 # Tests for 'git subtree merge'
 #
 
+test_expect_success 'merge rejects flags for split' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD
+	) &&
+	test_create_commit "$test_count/sub proj" sub2 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		test_wrong_flag git subtree merge --prefix="sub dir" --annotate=foo FETCH_HEAD &&
+		test_wrong_flag git subtree merge --prefix="sub dir" --branch=foo FETCH_HEAD &&
+		test_wrong_flag git subtree merge --prefix="sub dir" --ignore-joins FETCH_HEAD &&
+		test_wrong_flag git subtree merge --prefix="sub dir" --onto=foo FETCH_HEAD &&
+		test_wrong_flag git subtree merge --prefix="sub dir" --rejoin FETCH_HEAD
+	)
+'
+
 test_expect_success 'merge new subproj history into sub dir/ with --prefix' '
 	subtree_test_create_repo "$test_count" &&
 	subtree_test_create_repo "$test_count/sub proj" &&
@@ -262,6 +306,30 @@ test_expect_success 'split requires path given by option --prefix must exist' '
 	)
 '
 
+test_expect_success 'split rejects flags for add' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD
+	) &&
+	test_create_commit "$test_count" "sub dir"/main-sub1 &&
+	test_create_commit "$test_count" main2 &&
+	test_create_commit "$test_count/sub proj" sub2 &&
+	test_create_commit "$test_count" "sub dir"/main-sub2 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree merge --prefix="sub dir" FETCH_HEAD &&
+		split_hash=$(git subtree split --prefix="sub dir" --annotate="*") &&
+		test_wrong_flag git subtree split --prefix="sub dir" --squash &&
+		test_wrong_flag git subtree split --prefix="sub dir" --message=foo
+	)
+'
+
 test_expect_success 'split sub dir/ with --rejoin' '
 	subtree_test_create_repo "$test_count" &&
 	subtree_test_create_repo "$test_count/sub proj" &&
@@ -542,6 +610,26 @@ test_expect_success 'pull basic operation' '
 	)
 '
 
+test_expect_success 'pull rejects flags for split' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD
+	) &&
+	test_create_commit "$test_count/sub proj" sub2 &&
+	(
+		test_must_fail git subtree pull --prefix="sub dir" --annotate=foo ./"sub proj" HEAD &&
+		test_must_fail git subtree pull --prefix="sub dir" --branch=foo ./"sub proj" HEAD &&
+		test_must_fail git subtree pull --prefix="sub dir" --ignore-joins ./"sub proj" HEAD &&
+		test_must_fail git subtree pull --prefix="sub dir" --onto=foo ./"sub proj" HEAD &&
+		test_must_fail git subtree pull --prefix="sub dir" --rejoin ./"sub proj" HEAD
+	)
+'
+
 #
 # Tests for 'git subtree push'
 #
@@ -584,6 +672,29 @@ test_expect_success 'push requires path given by option --prefix must exist' '
 	)
 '
 
+test_expect_success 'push rejects flags for add' '
+	subtree_test_create_repo "$test_count" &&
+	subtree_test_create_repo "$test_count/sub proj" &&
+	test_create_commit "$test_count" main1 &&
+	test_create_commit "$test_count/sub proj" sub1 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree add --prefix="sub dir" FETCH_HEAD
+	) &&
+	test_create_commit "$test_count" "sub dir"/main-sub1 &&
+	test_create_commit "$test_count" main2 &&
+	test_create_commit "$test_count/sub proj" sub2 &&
+	test_create_commit "$test_count" "sub dir"/main-sub2 &&
+	(
+		cd "$test_count" &&
+		git fetch ./"sub proj" HEAD &&
+		git subtree merge --prefix="sub dir" FETCH_HEAD &&
+		test_wrong_flag git subtree split --prefix="sub dir" --squash ./"sub proj" from-mainline &&
+		test_wrong_flag git subtree split --prefix="sub dir" --message=foo ./"sub proj" from-mainline
+	)
+'
+
 test_expect_success 'push basic operation' '
 	subtree_test_create_repo "$test_count" &&
 	subtree_test_create_repo "$test_count/sub proj" &&