diff --git a/src/main/java/com/addthis/meshy/Main.java b/src/main/java/com/addthis/meshy/Main.java
index 1000a33..d810c51 100644
--- a/src/main/java/com/addthis/meshy/Main.java
+++ b/src/main/java/com/addthis/meshy/Main.java
@@ -51,8 +51,12 @@ public static void main(String args[]) throws Exception {
             try (Meshy more = new MeshyClient(args[1], Integer.parseInt(args[2]))) {
                 if (args.length > 3) {
                     String cmd = args[3];
-                    if (cmd.equals("ls") && args.length > 4) {
-                        FileSource fileSource = new FileSource(more, new String[]{args[4]});
+                    if (cmd.equals("ls")) {
+	                    String expr = args.length > 4 ? args[4] : "/*";
+	                    if (expr.endsWith("/")) {
+		                    expr += "*";
+	                    }
+                        FileSource fileSource = new FileSource(more, new String[]{expr});
                         fileSource.waitComplete();
                         for (FileReference file : fileSource.getFileList()) {
                             System.out.println(file.getHostUUID() + " " + file.name + " \t " + file.size + " \t " + new Date(file.lastModified));
diff --git a/src/main/java/com/addthis/meshy/service/message/MessageFileProvider.java b/src/main/java/com/addthis/meshy/service/message/MessageFileProvider.java
index 94d5921..a5cfd44 100644
--- a/src/main/java/com/addthis/meshy/service/message/MessageFileProvider.java
+++ b/src/main/java/com/addthis/meshy/service/message/MessageFileProvider.java
@@ -44,7 +44,10 @@ public void setListener(String fileName, MessageListener listener) {
             return;
         }
         synchronized (listeners) {
-            listeners.put(fileName, listener);
+            if (listeners.put(fileName, listener) != null) {
+                log.error("preventing override of file listener for {}", fileName);
+                return;
+            }
             OutputStream out = source.sendMessage(MessageFileSystem.MFS_ADD);
             try {
                 Bytes.writeString(fileName, out);
@@ -57,6 +60,10 @@ public void setListener(String fileName, MessageListener listener) {
 
     public void deleteListener(String fileName) {
         synchronized (listeners) {
+            if (listeners.remove(fileName) == null) {
+                log.error("attempting to remove absent listener for {}", fileName);
+                return;
+            }
             OutputStream out = source.sendMessage(MessageFileSystem.MFS_DEL);
             try {
                 Bytes.writeString(fileName, out);
@@ -64,7 +71,6 @@ public void deleteListener(String fileName) {
             } catch (Exception ex) {
                 throw new RuntimeException(ex);
             }
-            listeners.remove(fileName);
         }
     }