diff --git a/configure.in b/configure.in
index 186f80a5ec..207a4f1fde 100644
--- a/configure.in
+++ b/configure.in
@@ -3,7 +3,7 @@ AC_INIT
 AM_INIT_AUTOMAKE(tor, 0.0.2pre12)
 AM_CONFIG_HEADER(orconfig.h)
 
-CFLAGS="-Wall -O2 -I/usr/kerberos/include"
+CFLAGS="$CFLAGS -Wall -O2 -I/usr/kerberos/include"
 
 AC_ARG_ENABLE(debug,
 [  --enable-debug          compiles with debugging info],