diff --git a/amqp_relay.ml b/amqp_relay.ml
index 97c864a..c03c2e8 100644
--- a/amqp_relay.ml
+++ b/amqp_relay.ml
@@ -265,7 +265,7 @@ let handle_method conn channel m =
 						  Sexp.Str "Queue_declare_reply"))
   | Queue_bind (queue, exchange, routing_key, no_wait, arguments) ->
       let queue = expand_mrdq conn queue in
-      if not (Node.exists queue)
+      if not (Node.approx_exists queue)
       then send_warning conn not_found ("Queue "^queue^" not found")
       else
 	if Node.send exchange (Message.subscribe (Sexp.Str routing_key,
diff --git a/connections.ml b/connections.ml
index 5d71af2..d98eeae 100644
--- a/connections.ml
+++ b/connections.ml
@@ -3,6 +3,7 @@ open Printf
 open Thread
 open Sexp
 
+let connection_mtx = Mutex.create ()
 let connection_count = ref 0
 
 let endpoint_name n =
@@ -48,9 +49,9 @@ let connection_main class_name peername cin cout issue_banner boot_fn node_fn ma
 let start_connection' class_name issue_banner boot_fn node_fn mainloop (s, peername) =
   let cin = in_channel_of_descr s in
   let cout = out_channel_of_descr s in
-  connection_count := !connection_count + 1;
+  Util.with_mutex0 connection_mtx (fun () -> connection_count := !connection_count + 1);
   connection_main class_name peername cin cout issue_banner boot_fn node_fn mainloop;
-  connection_count := !connection_count - 1;
+  Util.with_mutex0 connection_mtx (fun () -> connection_count := !connection_count - 1);
   (try flush cout with _ -> ());
   close s
 
diff --git a/factory.ml b/factory.ml
index 8d3b02d..78f31e6 100644
--- a/factory.ml
+++ b/factory.ml
@@ -4,14 +4,17 @@ open Datastructures
 
 type factory_t = Sexp.t -> (Sexp.t, Sexp.t) Status.t
 
+let mutex = Mutex.create ()
 let classes = ref StringMap.empty
 
 let register_class name factory =
-  if StringMap.mem name !classes
-  then (Log.error "Duplicate node class name" [Str name];
-	exit 1)
-  else (Log.info "Registered node class" [Str name];
-	classes := StringMap.add name factory !classes)
+  Util.with_mutex0 mutex
+    (fun () ->
+      if StringMap.mem name !classes
+      then (Log.error "Duplicate node class name" [Str name];
+	    exit 1)
+      else (Log.info "Registered node class" [Str name];
+	    classes := StringMap.add name factory !classes))
 
 let lookup_class name =
   try Some (StringMap.find name !classes)
diff --git a/node.ml b/node.ml
index 294f0c2..1721a43 100644
--- a/node.ml
+++ b/node.ml
@@ -9,6 +9,7 @@ and t = {
     handle_message: handle_message_t
   }
 
+let mutex = Mutex.create ()
 let directory = ref StringMap.empty
 
 let local_container_name () = "server"
@@ -23,18 +24,21 @@ let lookup name =
   try Some (StringMap.find name !directory)
   with Not_found -> None
 
-let exists name = StringMap.mem name !directory
+(* Approximate because it doesn't lock or run in a transaction *)
+let approx_exists name = StringMap.mem name !directory
 
 let bind (filter, node) =
   if filter = ""
   then (Log.warn "Binding to empty name forbidden" []; false)
   else
-    if StringMap.mem filter !directory
-    then false
-    else (directory := StringMap.add filter node !directory;
-	  node.names <- StringSet.add filter node.names;
-	  Log.info "Node bound" [Sexp.Str filter; Sexp.Str node.class_name];
-	  true)
+    Util.with_mutex0 mutex
+      (fun () ->
+	if StringMap.mem filter !directory
+	then false
+	else (directory := StringMap.add filter node !directory;
+	      node.names <- StringSet.add filter node.names;
+	      Log.info "Node bound" [Sexp.Str filter; Sexp.Str node.class_name];
+	      true))
 
 (* For use in factory constructor functions, hence the odd return type and values *)
 let make_named class_name node_name handler =
@@ -53,14 +57,16 @@ let make_idempotent_named class_name node_name handler =
       if bind (node_name, node) then Ok node else Problem (Sexp.Str "bind-failed")
 
 let unbind name =
-  match lookup name with
-  | Some n ->
-      Log.info "Node unbound" [Sexp.Str name; Sexp.Str n.class_name];
-      n.names <- StringSet.remove name n.names;
-      directory := StringMap.remove name !directory;
-      true
-  | None ->
-      false
+  Util.with_mutex0 mutex
+    (fun () ->
+      match lookup name with
+      | Some n ->
+	  Log.info "Node unbound" [Sexp.Str name; Sexp.Str n.class_name];
+	  n.names <- StringSet.remove name n.names;
+	  directory := StringMap.remove name !directory;
+	  true
+      | None ->
+	  false)
 
 let unbind_all n =
   StringSet.iter (fun name -> ignore (unbind name)) n.names;