diff --git a/changes/bug1899_test_changed_addr b/changes/bug1899_test_changed_addr
new file mode 100644
index 0000000000..2823d3c6e0
--- /dev/null
+++ b/changes/bug1899_test_changed_addr
@@ -0,0 +1,4 @@
+  o Minor features
+    - When a router changes IP or port, authorities now launch a new
+      reachability test for it.  (Implements ticket 1899)
+
diff --git a/src/or/dirserv.c b/src/or/dirserv.c
index 523a92178e..b5c33739b3 100644
--- a/src/or/dirserv.c
+++ b/src/or/dirserv.c
@@ -3136,6 +3136,10 @@ dirserv_should_launch_reachability_test(routerinfo_t *ri, routerinfo_t *ri_old)
     /* It just came out of hibernation; launch a reachability test */
     return 1;
   }
+  if (ri_old->addr != ri->addr || ri_old->or_port != ri->or_port) {
+    /* Address or port changed; launch a reachability test */
+    return 1;
+  }
   return 0;
 }