diff -p -up gnac-0.2.4.1/configure.ac.cflags gnac-0.2.4.1/configure.ac
--- gnac-0.2.4.1/configure.ac.cflags	2012-12-06 00:08:36.198952786 +0100
+++ gnac-0.2.4.1/configure.ac	2012-12-06 00:44:56.921569739 +0100
@@ -125,9 +125,9 @@ fi
 # debug support
 AC_ARG_ENABLE([debug], [],
 [ if test "$enableval" = "yes"; then
-    CFLAGS="-g -ggdb -O0"
+    CFLAGS="$CFLAGS -g -ggdb -O0"
   else
-    CFLAGS="-O2"
+    CFLAGS="$CFLAGS -O2"
   fi
   AC_SUBST([CFLAGS])
   ])