diff --git a/Source/CPM3/Makefile b/Source/CPM3/Makefile
index c50b7ac6..bfb4d5f3 100644
--- a/Source/CPM3/Makefile
+++ b/Source/CPM3/Makefile
@@ -11,7 +11,8 @@ OTHERS += biosldrc.rel biosldrd.rel
 TOOLS = ../../Tools
 include $(TOOLS)/Makefile.inc
 
-export ZXINCDIR := ../
+ZXINCDIR = ../
+export ZXINCDIR
 
 BIOSOBJS = bioskrnl.rel scb.rel boot.rel chario.rel 
 BIOSOBJS += move.rel drvtbl.rel diskio.rel util.rel