diff --git a/vlib/os/const.v b/vlib/os/const.v
index 584a539347..25c5f7772c 100644
--- a/vlib/os/const.v
+++ b/vlib/os/const.v
@@ -80,6 +80,12 @@ const (
     O_TRUNC  = 128 // truncate regular writable file when opened.
 )
 
+// ref: http://www.ccfit.nsu.ru/~deviv/courses/unix/unix/ng7c229.html
+const (
+	S_IFMT  = 0xF000 // type of file
+	S_IFDIR = 0x4000 // directory
+)
+
 // Windows 
 const(
 	INVALID_HANDLE_VALUE = -1
diff --git a/vlib/os/os.v b/vlib/os/os.v
index c149bfb529..c1d27347c3 100644
--- a/vlib/os/os.v
+++ b/vlib/os/os.v
@@ -718,7 +718,8 @@ pub fn is_dir(path string) bool {
 		if C.stat(cstr, &statbuf) != 0 {
 			return false
 		}
-		return statbuf.st_mode & S_IFMT == S_IFDIR
+		// ref: https://code.woboq.org/gcc/include/sys/stat.h.html
+		return (statbuf.st_mode & S_IFMT) == S_IFDIR
 	} 
 }