diff --git a/builtin/stripspace.c b/builtin/stripspace.c
index 15e716ef43..1e62a008cb 100644
--- a/builtin/stripspace.c
+++ b/builtin/stripspace.c
@@ -44,8 +44,10 @@ int cmd_stripspace(int argc, const char **argv, const char *prefix)
 	if (argc)
 		usage_with_options(stripspace_usage, options);
 
-	if (mode == STRIP_COMMENTS || mode == COMMENT_LINES)
+	if (mode == STRIP_COMMENTS || mode == COMMENT_LINES) {
+		setup_git_directory_gently(NULL);
 		git_config(git_default_config, NULL);
+	}
 
 	if (strbuf_read(&buf, 0, 1024) < 0)
 		die_errno("could not read the input");
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index ca994c5c54..41fd374c72 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -93,8 +93,17 @@ eval '
 GIT_CHERRY_PICK_HELP="$resolvemsg"
 export GIT_CHERRY_PICK_HELP
 
-comment_char=$(git config --get core.commentchar 2>/dev/null | cut -c1)
-: ${comment_char:=#}
+comment_char=$(git config --get core.commentchar 2>/dev/null)
+case "$comment_char" in
+'' | auto)
+	comment_char="#"
+	;;
+?)
+	;;
+*)
+	comment_char=$(echo "$comment_char" | cut -c1)
+	;;
+esac
 
 warn () {
 	printf '%s\n' "$*" >&2
diff --git a/t/t0030-stripspace.sh b/t/t0030-stripspace.sh
index 29e91d861c..bbf3e39e3d 100755
--- a/t/t0030-stripspace.sh
+++ b/t/t0030-stripspace.sh
@@ -432,6 +432,15 @@ test_expect_success '-c with changed comment char' '
 	test_cmp expect actual
 '
 
+test_expect_success '-c with comment char defined in .git/config' '
+	test_config core.commentchar = &&
+	printf "= foo\n" >expect &&
+	printf "foo" | (
+		mkdir sub && cd sub && git stripspace -c
+	) >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'avoid SP-HT sequence in commented line' '
 	printf "#\tone\n#\n# two\n" >expect &&
 	printf "\tone\n\ntwo\n" | git stripspace -c >actual &&
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index e38e296388..c896a4c106 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -976,6 +976,17 @@ test_expect_success 'rebase -i respects core.commentchar' '
 	test B = $(git cat-file commit HEAD^ | sed -ne \$p)
 '
 
+test_expect_success 'rebase -i respects core.commentchar=auto' '
+	test_config core.commentchar auto &&
+	write_script copy-edit-script.sh <<-\EOF &&
+	cp "$1" edit-script
+	EOF
+	test_set_editor "$(pwd)/copy-edit-script.sh" &&
+	test_when_finished "git rebase --abort || :" &&
+	git rebase -i HEAD^ &&
+	test -z "$(grep -ve "^#" -e "^\$" -e "^pick" edit-script)"
+'
+
 test_expect_success 'rebase -i, with <onto> and <upstream> specified as :/quuxery' '
 	test_when_finished "git branch -D torebase" &&
 	git checkout -b torebase branch1 &&