diff --git a/abspath.c b/abspath.c
index b88122cbe7..c91a29cb29 100644
--- a/abspath.c
+++ b/abspath.c
@@ -54,8 +54,9 @@ const char *make_absolute_path(const char *path)
 			if (len + strlen(last_elem) + 2 > PATH_MAX)
 				die ("Too long path name: '%s/%s'",
 						buf, last_elem);
-			buf[len] = '/';
-			strcpy(buf + len + 1, last_elem);
+			if (len && buf[len-1] != '/')
+				buf[len++] = '/';
+			strcpy(buf + len, last_elem);
 			free(last_elem);
 			last_elem = NULL;
 		}
diff --git a/builtin-init-db.c b/builtin-init-db.c
index dd84caecbc..aae7a4d7ee 100644
--- a/builtin-init-db.c
+++ b/builtin-init-db.c
@@ -331,11 +331,14 @@ int init_db(const char *template_dir, unsigned int flags)
 		git_config_set("receive.denyNonFastforwards", "true");
 	}
 
-	if (!(flags & INIT_DB_QUIET))
-		printf("%s%s Git repository in %s/\n",
+	if (!(flags & INIT_DB_QUIET)) {
+		const char *git_dir = get_git_dir();
+		int len = strlen(git_dir);
+		printf("%s%s Git repository in %s%s\n",
 		       reinit ? "Reinitialized existing" : "Initialized empty",
 		       shared_repository ? " shared" : "",
-		       get_git_dir());
+		       git_dir, len && git_dir[len-1] != '/' ? "/" : "");
+	}
 
 	return 0;
 }
diff --git a/builtin-rev-parse.c b/builtin-rev-parse.c
index a8c5043ded..88bad9af3c 100644
--- a/builtin-rev-parse.c
+++ b/builtin-rev-parse.c
@@ -637,6 +637,7 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 			if (!strcmp(arg, "--git-dir")) {
 				const char *gitdir = getenv(GIT_DIR_ENVIRONMENT);
 				static char cwd[PATH_MAX];
+				int len;
 				if (gitdir) {
 					puts(gitdir);
 					continue;
@@ -647,7 +648,8 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				}
 				if (!getcwd(cwd, PATH_MAX))
 					die_errno("unable to get current working directory");
-				printf("%s/.git\n", cwd);
+				len = strlen(cwd);
+				printf("%s%s.git\n", cwd, len && cwd[len-1] != '/' ? "/" : "");
 				continue;
 			}
 			if (!strcmp(arg, "--is-inside-git-dir")) {
diff --git a/cache.h b/cache.h
index 4d89aa3da4..c286310ded 100644
--- a/cache.h
+++ b/cache.h
@@ -679,6 +679,7 @@ int normalize_path_copy(char *dst, const char *src);
 int longest_ancestor_length(const char *path, const char *prefix_list);
 char *strip_path_suffix(const char *path, const char *suffix);
 int daemon_avoid_alias(const char *path);
+int offset_1st_component(const char *path);
 
 /* Read and unpack a sha1 file into memory, write memory to a sha1 file */
 extern int sha1_object_info(const unsigned char *, unsigned long *);
diff --git a/path.c b/path.c
index c290e74486..b4c8d91722 100644
--- a/path.c
+++ b/path.c
@@ -728,3 +728,10 @@ int daemon_avoid_alias(const char *p)
 		}
 	}
 }
+
+int offset_1st_component(const char *path)
+{
+	if (has_dos_drive_prefix(path))
+		return 2 + is_dir_sep(path[2]);
+	return is_dir_sep(path[0]);
+}
diff --git a/setup.c b/setup.c
index 0717a98d16..5716d90b57 100644
--- a/setup.c
+++ b/setup.c
@@ -18,14 +18,15 @@ const char *prefix_path(const char *prefix, int len, const char *path)
 	if (normalize_path_copy(sanitized, sanitized))
 		goto error_out;
 	if (is_absolute_path(orig)) {
-		size_t len, total;
+		size_t root_len, len, total;
 		const char *work_tree = get_git_work_tree();
 		if (!work_tree)
 			goto error_out;
 		len = strlen(work_tree);
+		root_len = offset_1st_component(work_tree);
 		total = strlen(sanitized) + 1;
 		if (strncmp(sanitized, work_tree, len) ||
-		    (sanitized[len] != '\0' && sanitized[len] != '/')) {
+		    (len > root_len && sanitized[len] != '\0' && sanitized[len] != '/')) {
 		error_out:
 			die("'%s' is outside repository", orig);
 		}
@@ -321,7 +322,7 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	static char cwd[PATH_MAX+1];
 	const char *gitdirenv;
 	const char *gitfile_dir;
-	int len, offset, ceil_offset;
+	int len, offset, ceil_offset, root_len;
 
 	/*
 	 * Let's assume that we are in a git repository.
@@ -403,7 +404,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 			if (!work_tree_env)
 				inside_work_tree = 0;
 			if (offset != len) {
-				cwd[offset] = '\0';
+				root_len = offset_1st_component(cwd);
+				cwd[offset > root_len ? offset : root_len] = '\0';
 				set_git_dir(cwd);
 			} else
 				set_git_dir(".");
@@ -427,7 +429,8 @@ const char *setup_git_directory_gently(int *nongit_ok)
 	inside_git_dir = 0;
 	if (!work_tree_env)
 		inside_work_tree = 1;
-	git_work_tree_cfg = xstrndup(cwd, offset);
+	root_len = offset_1st_component(cwd);
+	git_work_tree_cfg = xstrndup(cwd, offset > root_len ? offset : root_len);
 	if (check_repository_format_gently(nongit_ok))
 		return NULL;
 	if (offset == len)
diff --git a/sha1_file.c b/sha1_file.c
index c23cc5e6e1..a08a9d0880 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -35,13 +35,6 @@ static size_t sz_fmt(size_t s) { return s; }
 
 const unsigned char null_sha1[20];
 
-static inline int offset_1st_component(const char *path)
-{
-	if (has_dos_drive_prefix(path))
-		return 2 + (path[2] == '/');
-	return *path == '/';
-}
-
 int safe_create_leading_directories(char *path)
 {
 	char *pos = path + offset_1st_component(path);
diff --git a/t/t1509-root-worktree.sh b/t/t1509-root-worktree.sh
new file mode 100755
index 0000000000..5322a3bf97
--- /dev/null
+++ b/t/t1509-root-worktree.sh
@@ -0,0 +1,249 @@
+#!/bin/sh
+
+test_description='Test Git when git repository is located at root
+
+This test requires write access in root. Do not bother if you do not
+have a throwaway chroot or VM.
+
+Script t1509/prepare-chroot.sh may help you setup chroot, then you
+can chroot in and execute this test from there.
+'
+
+. ./test-lib.sh
+
+test_cmp_val() {
+	echo "$1" > expected
+	echo "$2" > result
+	test_cmp expected result
+}
+
+test_vars() {
+	test_expect_success "$1: gitdir" '
+		test_cmp_val "'"$2"'" "$(git rev-parse --git-dir)"
+	'
+
+	test_expect_success "$1: worktree" '
+		test_cmp_val "'"$3"'" "$(git rev-parse --show-toplevel)"
+	'
+
+	test_expect_success "$1: prefix" '
+		test_cmp_val "'"$4"'" "$(git rev-parse --show-prefix)"
+	'
+}
+
+test_foobar_root() {
+	test_expect_success 'add relative' '
+		test -z "$(cd / && git ls-files)" &&
+		git add foo/foome &&
+		git add foo/bar/barme &&
+		git add me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+
+	test_expect_success 'add absolute' '
+		test -z "$(cd / && git ls-files)" &&
+		git add /foo/foome &&
+		git add /foo/bar/barme &&
+		git add /me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+
+}
+
+test_foobar_foo() {
+	test_expect_success 'add relative' '
+		test -z "$(cd / && git ls-files)" &&
+		git add foome &&
+		git add bar/barme &&
+		git add ../me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+
+	test_expect_success 'add absolute' '
+		test -z "$(cd / && git ls-files)" &&
+		git add /foo/foome &&
+		git add /foo/bar/barme &&
+		git add /me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+}
+
+test_foobar_foobar() {
+	test_expect_success 'add relative' '
+		test -z "$(cd / && git ls-files)" &&
+		git add ../foome &&
+		git add barme &&
+		git add ../../me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+
+	test_expect_success 'add absolute' '
+		test -z "$(cd / && git ls-files)" &&
+		git add /foo/foome &&
+		git add /foo/bar/barme &&
+		git add /me &&
+		( cd / && git ls-files --stage ) > result &&
+		test_cmp /ls.expected result &&
+		rm "$(git rev-parse --git-dir)/index"
+	'
+}
+
+if ! test_have_prereq POSIXPERM || ! [ -w / ]; then
+	say "Dangerous test skipped. Read this test if you want to execute it"
+	test_done
+fi
+
+if [ "$IKNOWWHATIAMDOING" != "YES" ]; then
+	say "You must set env var IKNOWWHATIAMDOING=YES in order to run this test"
+	test_done
+fi
+
+if [ "$UID" = 0 ]; then
+	say "No you can't run this with root"
+	test_done
+fi
+
+ONE_SHA1=d00491fd7e5bb6fa28c517a0bb32b8b506539d4d
+
+test_expect_success 'setup' '
+	rm -rf /foo
+	mkdir /foo &&
+	mkdir /foo/bar &&
+	echo 1 > /foo/foome &&
+	echo 1 > /foo/bar/barme &&
+	echo 1 > /me
+'
+
+say "GIT_DIR absolute, GIT_WORK_TREE set"
+
+test_expect_success 'go to /' 'cd /'
+
+cat >ls.expected <<EOF
+100644 $ONE_SHA1 0	foo/bar/barme
+100644 $ONE_SHA1 0	foo/foome
+100644 $ONE_SHA1 0	me
+EOF
+
+export GIT_DIR="$TRASH_DIRECTORY/.git"
+export GIT_WORK_TREE=/
+
+test_vars 'abs gitdir, root' "$GIT_DIR" "/" ""
+test_foobar_root
+
+test_expect_success 'go to /foo' 'cd /foo'
+
+test_vars 'abs gitdir, foo' "$GIT_DIR" "/" "foo/"
+test_foobar_foo
+
+test_expect_success 'go to /foo/bar' 'cd /foo/bar'
+
+test_vars 'abs gitdir, foo/bar' "$GIT_DIR" "/" "foo/bar/"
+test_foobar_foobar
+
+say "GIT_DIR relative, GIT_WORK_TREE set"
+
+test_expect_success 'go to /' 'cd /'
+
+export GIT_DIR="$(echo $TRASH_DIRECTORY|sed 's,^/,,')/.git"
+export GIT_WORK_TREE=/
+
+test_vars 'rel gitdir, root' "$GIT_DIR" "/" ""
+test_foobar_root
+
+test_expect_success 'go to /foo' 'cd /foo'
+
+export GIT_DIR="../$TRASH_DIRECTORY/.git"
+export GIT_WORK_TREE=/
+
+test_vars 'rel gitdir, foo' "$TRASH_DIRECTORY/.git" "/" "foo/"
+test_foobar_foo
+
+test_expect_success 'go to /foo/bar' 'cd /foo/bar'
+
+export GIT_DIR="../../$TRASH_DIRECTORY/.git"
+export GIT_WORK_TREE=/
+
+test_vars 'rel gitdir, foo/bar' "$TRASH_DIRECTORY/.git" "/" "foo/bar/"
+test_foobar_foobar
+
+say "GIT_DIR relative, GIT_WORK_TREE relative"
+
+test_expect_success 'go to /' 'cd /'
+
+export GIT_DIR="$(echo $TRASH_DIRECTORY|sed 's,^/,,')/.git"
+export GIT_WORK_TREE=.
+
+test_vars 'rel gitdir, root' "$GIT_DIR" "/" ""
+test_foobar_root
+
+test_expect_success 'go to /' 'cd /foo'
+
+export GIT_DIR="../$TRASH_DIRECTORY/.git"
+export GIT_WORK_TREE=..
+
+test_vars 'rel gitdir, foo' "$TRASH_DIRECTORY/.git" "/" "foo/"
+test_foobar_foo
+
+test_expect_success 'go to /foo/bar' 'cd /foo/bar'
+
+export GIT_DIR="../../$TRASH_DIRECTORY/.git"
+export GIT_WORK_TREE=../..
+
+test_vars 'rel gitdir, foo/bar' "$TRASH_DIRECTORY/.git" "/" "foo/bar/"
+test_foobar_foobar
+
+say ".git at root"
+
+unset GIT_DIR
+unset GIT_WORK_TREE
+
+test_expect_success 'go to /' 'cd /'
+test_expect_success 'setup' '
+	rm -rf /.git
+	echo "Initialized empty Git repository in /.git/" > expected &&
+	git init > result &&
+	test_cmp expected result
+'
+
+test_vars 'auto gitdir, root' ".git" "/" ""
+test_foobar_root
+
+test_expect_success 'go to /foo' 'cd /foo'
+test_vars 'auto gitdir, foo' "/.git" "/" "foo/"
+test_foobar_foo
+
+test_expect_success 'go to /foo/bar' 'cd /foo/bar'
+test_vars 'auto gitdir, foo/bar' "/.git" "/" "foo/bar/"
+test_foobar_foobar
+
+test_expect_success 'cleanup' 'rm -rf /.git'
+
+say "auto bare gitdir"
+
+# DESTROYYYYY!!!!!
+test_expect_success 'setup' '
+	rm -rf /refs /objects /info /hooks
+	rm /*
+	cd / &&
+	echo "Initialized empty Git repository in /" > expected &&
+	git init --bare > result &&
+	test_cmp expected result
+'
+
+test_vars 'auto gitdir, root' "." "" ""
+
+test_expect_success 'go to /foo' 'cd /foo'
+
+test_vars 'auto gitdir, root' "/" "" ""
+
+test_done
diff --git a/t/t1509/excludes b/t/t1509/excludes
new file mode 100644
index 0000000000..d4d21d31a9
--- /dev/null
+++ b/t/t1509/excludes
@@ -0,0 +1,14 @@
+*.o
+*~
+*.bak
+*.c
+*.h
+.git
+contrib
+Documentation
+git-gui
+gitk-git
+gitweb
+t/t4013
+t/t5100
+t/t5515
diff --git a/t/t1509/prepare-chroot.sh b/t/t1509/prepare-chroot.sh
new file mode 100755
index 0000000000..c5334a8fa4
--- /dev/null
+++ b/t/t1509/prepare-chroot.sh
@@ -0,0 +1,38 @@
+#!/bin/sh
+
+die() {
+	echo >&2 "$@"
+	exit 1
+}
+
+xmkdir() {
+	while [ -n "$1" ]; do
+		[ -d "$1" ] || mkdir "$1" || die "Unable to mkdir $1"
+		shift
+	done
+}
+
+R="$1"
+
+[ -n "$R" ] || die "Usage: prepare-chroot.sh <root>"
+[ -x git ] || die "This script needs to be executed at git source code's top directory"
+[ -x /bin/busybox ] || die "You need busybox"
+
+xmkdir "$R" "$R/bin" "$R/etc" "$R/lib" "$R/dev"
+[ -c "$R/dev/null" ] || die "/dev/null is missing. Do mknod $R/dev/null c 1 3 && chmod 666 $R/dev/null"
+echo "root:x:0:0:root:/:/bin/sh" > "$R/etc/passwd"
+echo "$(id -nu):x:$(id -u):$(id -g)::$(pwd)/t:/bin/sh" >> "$R/etc/passwd"
+echo "root::0:root" > "$R/etc/group"
+echo "$(id -ng)::$(id -g):$(id -nu)" >> "$R/etc/group"
+
+[ -x "$R/bin/busybox" ] || cp /bin/busybox "$R/bin/busybox"
+[ -x "$R/bin/sh" ] || ln -s /bin/busybox "$R/bin/sh"
+[ -x "$R/bin/su" ] || ln -s /bin/busybox "$R/bin/su"
+
+mkdir -p "$R$(pwd)"
+rsync --exclude-from t/t1509/excludes -Ha . "$R$(pwd)"
+ldd git | grep '/' | sed 's,.*\s\(/[^ ]*\).*,\1,' | while read i; do
+	mkdir -p "$R$(dirname $i)"
+	cp "$i" "$R/$i"
+done
+echo "Execute this in root: 'chroot $R /bin/su - $(id -nu)'"