diff --git a/src/codechicken/lib/packet/PacketCustom.java b/src/codechicken/lib/packet/PacketCustom.java
index 7e238f2..bd4586b 100644
--- a/src/codechicken/lib/packet/PacketCustom.java
+++ b/src/codechicken/lib/packet/PacketCustom.java
@@ -145,8 +145,12 @@ public final class PacketCustom implements MCDataInput, MCDataOutput
     public static String channelName(Object channelKey) {
         if (channelKey instanceof String)
             return (String) channelKey;
-        if (channelKey instanceof ModContainer)
-            return ((ModContainer) channelKey).getModId();
+        if (channelKey instanceof ModContainer) {
+            String s = ((ModContainer) channelKey).getModId();
+            if(s.length() > 20)
+                throw new IllegalArgumentException("Mod ID ("+s+") too long for use as channel (20 chars). Use a string identifier");
+            return s;
+        }
 
         ModContainer mc = FMLCommonHandler.instance().findContainerFor(channelKey);
         if (mc != null)