diff --git a/auto/cc b/auto/cc
index 082b13f..6edae88 100644
--- a/auto/cc
+++ b/auto/cc
@@ -24,7 +24,7 @@
          # debug
          CFLAGS="$CFLAGS -g"
 
-         CFLAGS="$CFLAGS -D HAVE_GCC_VARIADIC_MACROS=1"
+         have=HAVE_GCC_VARIADIC_MACROS . auto/have
 
          OBJEXT=o
          OBJOUT="-o "
@@ -50,7 +50,7 @@
          # stop on warning
          CFLAGS="$CFLAGS -Werror"
 
-         CFLAGS="$CFLAGS -D HAVE_C99_VARIADIC_MACROS=1"
+         have=HAVE_C99_VARIADIC_MACROS . auto/have
 
          OBJEXT=o
          OBJOUT="-o "