--- a/configure.in
+++ b/configure.in
@@ -2,7 +2,7 @@
 AM_INIT_AUTOMAKE(shed,1.15)
 AC_PROG_CC
 AC_PROG_INSTALL
-CFLAGS="-Wall"
+CFLAGS="$CFLAGS -Wall"
 AC_SUBST(CFLAGS)
 
 AC_ARG_ENABLE(debug,   [  --enable-debug          gcc -g],enable_debug=yes)