diff --git a/mach/xenix3/libsys/signal.s b/mach/xenix3/libsys/signal.s
index b953a1a82..e3d3b0dc0 100644
--- a/mach/xenix3/libsys/signal.s
+++ b/mach/xenix3/libsys/signal.s
@@ -56,8 +56,11 @@ ctch:
 	push	si
 	push	di
 	mov	ax,2(bp)
+	sub	ax,3
 	sub	ax,tbl
 	shr	ax,1
+	mov	bx,ax
+	shr	ax,1
 	push	ax
 	call	table(bx)
 	pop	di