diff --git a/mach/z80/libpc/compmodule b/mach/z80/libpc/compmodule
index 284613267..4a77cd8a0 100755
--- a/mach/z80/libpc/compmodule
+++ b/mach/z80/libpc/compmodule
@@ -1,2 +1,2 @@
-${MACH?} -I../../../h ${MACHFL?} $1 1>&2
+${MACH?} -DCPM -I../../../h ${MACHFL?} $1 1>&2
 echo `basename $1 $2`.s