diff --git a/configure.ac b/configure.ac
index f4937170..d6378d03 100644
--- a/configure.ac
+++ b/configure.ac
@@ -40,7 +40,10 @@ AC_DEFUN([TEST_AND_ADD_CFLAGS],
           dnl Note AC_LANG_PROGRAM([]) uses an old-style main definition.
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([int main(void) { return 0; }])],
                             [AC_MSG_RESULT([yes])]
-                            [AS_VAR_APPEND([AM_CFLAGS], [" $1"])],
+                            dnl Simply append the variable avoiding a
+                            dnl compatibility ifdef for AS_VAR_APPEND as this
+                            dnl variable shouldn't grow all that large.
+                            [AM_CFLAGS="$AM_CFLAGS $1"],
                             [AC_MSG_RESULT([no])])
           CFLAGS="$SAVED_CFLAGS"])
 TEST_AND_ADD_CFLAGS([-Wall])