diff --git a/vlib/os/os.v b/vlib/os/os.v
index 82692ed255..a7d09625a9 100644
--- a/vlib/os/os.v
+++ b/vlib/os/os.v
@@ -535,7 +535,8 @@ pub fn log(s string) {
 }
 
 // mkdir_all will create a valid full path of all directories given in `path`.
-pub fn mkdir_all(path string) ? {
+pub fn mkdir_all(opath string) ? {
+	path := opath.replace('/', path_separator)
 	mut p := if path.starts_with(path_separator) { path_separator } else { '' }
 	path_parts := path.trim_left(path_separator).split(path_separator)
 	for subdir in path_parts {
diff --git a/vlib/os/os_test.v b/vlib/os/os_test.v
index 7cdca800c9..26bea76805 100644
--- a/vlib/os/os_test.v
+++ b/vlib/os/os_test.v
@@ -201,6 +201,8 @@ fn test_ls() {
 fn create_tree() ? {
 	os.mkdir_all('myfolder/f1/f2/f3') ?
 	os.mkdir_all('myfolder/a1/a2/a3') ?
+	f3 := os.real_path('myfolder/f1/f2/f3')
+	assert os.is_dir(f3)
 	create_file('myfolder/f1/f2/f3/a.txt') ?
 	create_file('myfolder/f1/f2/f3/b.txt') ?
 	create_file('myfolder/f1/f2/f3/c.txt') ?