diff --git a/Source/CBIOS/cbios.asm b/Source/CBIOS/cbios.asm
index ae670c67..98cf9510 100644
--- a/Source/CBIOS/cbios.asm
+++ b/Source/CBIOS/cbios.asm
@@ -3381,7 +3381,7 @@ DEVUNK		.DB	"UNK$"
 	RST	08		; CALL HBIOS
 	LD	A,D		; RESULTANT DEVICE TYPE
 	PUSH	DE		; NEED TO SAVE UNIT NUMBER (IN E)
-	AND	$0F		; ISOLATE DEVICE BITS
+	AND	$1F		; ISOLATE DEVICE BITS
 	ADD	A,A		; MULTIPLY BY TWO FOR WORD TABLE
 	LD	HL,DEVTBL	; POINT TO START OF DEVICE NAME TABLE
 	CALL	ADDHLA		; ADD A TO HL TO POINT TO TABLE ENTRY