diff --git a/drivers/staging/sb105x/sb_mp_register.h b/drivers/staging/sb105x/sb_mp_register.h
index 5480ae11368f..a2087f5b0d1a 100644
--- a/drivers/staging/sb105x/sb_mp_register.h
+++ b/drivers/staging/sb105x/sb_mp_register.h
@@ -45,7 +45,7 @@
 #define IIR_RS232		0x00		/* RS232 type */
 #define IIR_RS422		0x10		/* RS422 type */
 #define IIR_RS485		0x20		/* RS485 type */
-#define IIR_UNKNOWN		0x30		/* unknown type */
+#define IIR_TYPE_MASK		0x30
 
 /* Interrrupt Mask Register */
 #define MP_OPTR_IMR0		0x0C 	/* port0 ~ port8 */
diff --git a/drivers/staging/sb105x/sb_pci_mp.c b/drivers/staging/sb105x/sb_pci_mp.c
index c34ebff6bb04..3da44dff24bf 100644
--- a/drivers/staging/sb105x/sb_pci_mp.c
+++ b/drivers/staging/sb105x/sb_pci_mp.c
@@ -2851,18 +2851,12 @@ static void __init multi_init_ports(void)
 				printk("IIR_RET = %x\n",b_ret);
 			}
 
-			if(IIR_RS232 == (b_ret & IIR_RS232))
-			{
-				mtpt->interface = RS232;
-			}
-			if(IIR_RS422 == (b_ret & IIR_RS422))
-			{
+			/* default to RS232 */
+			mtpt->interface = RS232;
+			if (IIR_RS422 == (b_ret & IIR_TYPE_MASK))
 				mtpt->interface = RS422PTP;
-			}
-			if(IIR_RS485 == (b_ret & IIR_RS485))
-			{
+			if (IIR_RS485 == (b_ret & IIR_TYPE_MASK))
 				mtpt->interface = RS485NE;
-			}
 		}
 	}
 }