diff --git a/apps/Makefile b/apps/Makefile
index 150da4a..0d03239 100644
--- a/apps/Makefile
+++ b/apps/Makefile
@@ -27,6 +27,15 @@ C64_DRIVERLIB = ../drivers/ip65_c64.lib
 A2_DRIVERLIB  = ../drivers/ip65_apple2.lib
 ATR_DRIVERLIB = ../drivers/ip65_atari.lib
 
+# See http://vice-emu.sourceforge.net/
+C1541 ?= c1541
+
+# See https://applecommander.github.io/
+AC ?= ac.jar
+
+# See https://www.horus.com/~hias/atari/
+DIR2ATR ?= dir2atr
+
 UDP =\
 	date65
 
diff --git a/test/Makefile b/test/Makefile
index ade6fef..cd10c21 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -25,6 +25,15 @@ else
   VICDRIVERLIB = ../drivers/vic20rrnet.lib
 endif
 
+# See http://vice-emu.sourceforge.net/
+C1541 ?= c1541
+
+# See https://applecommander.github.io/
+AC ?= ac.jar
+
+# See https://www.horus.com/~hias/atari/
+DIR2ATR ?= dir2atr
+
 UDP =\
 	dns \
 	dottedquad \