diff --git a/libsrc/geos-cbm/devel/mainargs.s b/libsrc/geos-cbm/devel/mainargs.s
index 5474dc589..6f27a4e93 100644
--- a/libsrc/geos-cbm/devel/mainargs.s
+++ b/libsrc/geos-cbm/devel/mainargs.s
@@ -37,7 +37,11 @@
 	ldy	#0
 @fn_loop:
 	lda	dirEntryBuf+OFF_FNAME,y
+.ifdef  __GEOS_CBM__
 	cmp	#$a0
+.else
+	cmp	#0
+.endif
 	beq	@fn_end
 	sta	argv0,y
 	iny