diff --git a/source/org/jivesoftware/smack/PacketListener.java b/source/org/jivesoftware/smack/PacketListener.java
index 6f3a00c8a..26553b320 100644
--- a/source/org/jivesoftware/smack/PacketListener.java
+++ b/source/org/jivesoftware/smack/PacketListener.java
@@ -68,7 +68,11 @@ import org.jivesoftware.smack.filter.PacketFilter;
 public interface PacketListener {
 
     /**
-     * Process the next packet sent to this packet listener.
+     * Process the next packet sent to this packet listener.<p>
+     *
+     * A single thread is responsible for invoking all listeners, so
+     * it's very important that implementations of this method not block
+     * for any extended period of time.
      *
      * @param packet the packet to process.
      */