diff --git a/src/config.in b/src/config.in
index 09bc0ba6629..5f3f5930e39 100644
--- a/src/config.in
+++ b/src/config.in
@@ -301,6 +301,7 @@ Boston, MA 02111-1307, USA.  */
 #undef HAVE_STRUCT_TIMEZONE
 #undef HAVE_INDEX
 #undef HAVE_RINDEX
+#undef HAVE_MMAP
 
 #undef LOCALTIME_CACHE
 #undef HAVE_INET_SOCKETS