Index: modules/metadata/mod_expires.c
===================================================================
--- modules/metadata/mod_expires.c	(revision 570093)
+++ modules/metadata/mod_expires.c	(revision 713142)
@@ -430,6 +430,9 @@
     }
 
     expires = base + additional;
+    if (expires < r->request_time) {
+        expires = r->request_time;
+    }
     apr_table_mergen(t, "Cache-Control",
                      apr_psprintf(r->pool, "max-age=%" APR_TIME_T_FMT,
                                   apr_time_sec(expires - r->request_time)));