diff --git a/disk/part_dos.c b/disk/part_dos.c
index ef706fb59c..20d35dc9cd 100644
--- a/disk/part_dos.c
+++ b/disk/part_dos.c
@@ -42,9 +42,9 @@ static inline unsigned int le32_to_int(unsigned char *le32)
 
 static inline int is_extended(int part_type)
 {
-    return (part_type == 0x5 ||
-	    part_type == 0xf ||
-	    part_type == 0x85);
+    return (part_type == DOS_PART_TYPE_EXTENDED ||
+	    part_type == DOS_PART_TYPE_EXTENDED_LBA ||
+	    part_type == DOS_PART_TYPE_EXTENDED_LINUX);
 }
 
 static int get_bootable(dos_partition_t *p)
diff --git a/disk/part_dos.h b/disk/part_dos.h
index 434b021ae8..dd909a9317 100644
--- a/disk/part_dos.h
+++ b/disk/part_dos.h
@@ -15,6 +15,9 @@
 #define DOS_PBR_MEDIA_TYPE_OFFSET	0x15
 #define DOS_MBR	0
 #define DOS_PBR	1
+#define DOS_PART_TYPE_EXTENDED		0x05
+#define DOS_PART_TYPE_EXTENDED_LBA	0x0F
+#define DOS_PART_TYPE_EXTENDED_LINUX	0x85
 
 typedef struct dos_partition {
 	unsigned char boot_ind;		/* 0x80 - active			*/