diff --git a/evm/Makefile b/evm/Makefile
index 7e6c5ff..f40f1a4 100644
--- a/evm/Makefile
+++ b/evm/Makefile
@@ -1,6 +1,7 @@
 CC = gcc
 #CFLAGS = -Wall -g -DUSE_BOEHM
-CFLAGS = -Wall -O3 -DUSE_BOEHM
+CFLAGS ?= -Wall -O3
+CFLAGS += -DUSE_BOEHM
 OBJS = closure.o stdfuns.o emalloc.o sparks.o
 INSTALLDIR = ${PREFIX}/lib/evm
 
