diff --git a/app.py b/app.py
index a8a184a..e4dae99 100644
--- a/app.py
+++ b/app.py
@@ -97,8 +97,9 @@ def verify_node(d):
     if "/" in node:
         raise ValueError("invalid node name %s", node)
     try:
-        log.info("getting client config from %s", "config/" + node)
-        with open("config/" + node) as fh:
+        fn = "config/" + node
+        log.info("getting client config from %s", fn)
+        with open(fn) as fh:
             node_conf = json.load(fh)
     except Exception as e:
         log.warning("got %s opening %s", e, "config/" + node)
@@ -112,8 +113,19 @@ def verify_node(d):
             if timestamp > node_conf["last"]:
                 node_conf["last"] = timestamp
                 os.replace("config/" + node, "config/" + node + ".old")
-                with open("config/" + node, "w") as fh:
+                tmpfn = fn + "." + str(os.getpid())
+                oldfn = fn + ".old"
+                with open(tmpfn, "w") as fh:
                     json.dump(node_conf, fh) # XXX
+                try:
+                    os.unlink(oldfn)
+                except FileNotFoundError:
+                    pass
+                try:
+                    os.link(fn, oldfn)
+                except FileNotFoundError:
+                    pass
+                os.rename(tmpfn, fn)
                 return node
             else:
                 abort(409, "timestamp out of sync")