Index: src/or/rendservice.c
===================================================================
--- src/or/rendservice.c	(revision 17386)
+++ src/or/rendservice.c	(working copy)
@@ -291,9 +291,10 @@
   config_line_t *line;
   rend_service_t *service = NULL;
   rend_service_port_config_t *portcfg;
+  smartlist_t *old_service_list = NULL;
 
   if (!validate_only) {
-    rend_service_free_all();
+    old_service_list = rend_service_list;
     rend_service_list = smartlist_create();
   }
 
@@ -473,6 +474,25 @@
       rend_add_service(service);
   }
 
+  if (old_service_list && !validate_only) {
+    strmap_t *old_service_by_dir = strmap_new();
+    SMARTLIST_FOREACH(old_service_list, rend_service_t *, ptr,
+                      strmap_set(old_service_by_dir, ptr->directory, ptr));
+    SMARTLIST_FOREACH(rend_service_list, rend_service_t *, ptr,
+      {
+        rend_service_t *old = strmap_get(old_service_by_dir, ptr->directory);
+        if (old) {
+          smartlist_add_all(ptr->intro_nodes, old->intro_nodes);
+          smartlist_clear(old->intro_nodes);
+        }
+      });
+
+    strmap_free(old_service_by_dir, NULL);
+    SMARTLIST_FOREACH(old_service_list, rend_service_t *, ptr,
+                      rend_service_free(ptr));
+    smartlist_free(old_service_list);
+  }
+
   return 0;
 }