diff --git a/sys/i386/isa/wcd.c b/sys/i386/isa/wcd.c
index 901382e180d..76cb6407dfa 100644
--- a/sys/i386/isa/wcd.c
+++ b/sys/i386/isa/wcd.c
@@ -36,7 +36,7 @@
 #include <i386/isa/atapi.h>
 
 #define NUNIT   (NWDC*2)        /* Max. number of devices */
-#define UNIT(d) (minor(d) & 3)  /* Unit part of minor device number */
+#define UNIT(d) ((minor(d) >> 3) & 3)  /* Unit part of minor device number */
 #define SECSIZE 2048            /* CD-ROM sector size in bytes */
 
 #define F_OPEN          0x0001  /* The drive os opened */