--- a/src/Makefile
+++ b/src/Makefile
@@ -1,7 +1,7 @@
 # In case of windows, use os_cygwin=yes setting in the configuration file (smsd.conf).
 
 # Select your setup size:
-CFLAGS = -D NUMBER_OF_MODEMS=64
+CFLAGS ?= -D NUMBER_OF_MODEMS=64
 
 # Uncomment for Solaris
 # CFLAGS += -D SOLARIS
