diff --git a/Makefile b/Makefile
index 78fa5386..34f5d403 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,8 @@
 TARGET ?= PicoDrive
+DEBUG ?= 0
 CFLAGS += -Wall -g
 CFLAGS += -I.
-ifndef DEBUG
+ifeq "$(DEBUG)" "0"
 CFLAGS += -O3 -DNDEBUG
 endif