diff --git a/src/java/com/threerings/presents/tools/GenServiceTask.java b/src/java/com/threerings/presents/tools/GenServiceTask.java
index b775b6aee..45d9bbd1c 100644
--- a/src/java/com/threerings/presents/tools/GenServiceTask.java
+++ b/src/java/com/threerings/presents/tools/GenServiceTask.java
@@ -62,6 +62,12 @@ public class GenServiceTask extends InvocationTask
             return getName().compareTo(other.getName());
         }
 
+        public boolean equals (Object other)
+        {
+            return getClass().equals(other.getClass()) &&
+                listener.equals(((ServiceListener)other).listener);
+        }
+
         public String getName ()
         {
             String name = simpleName(listener);
@@ -113,8 +119,8 @@ public class GenServiceTask extends InvocationTask
             for (int aa = 0; aa < args.length; aa++) {
                 if (_ilistener.isAssignableFrom(args[aa]) &&
                     simpleName(args[aa]).startsWith(sname + ".")) {
-                    listeners.add(new ServiceListener(
-                                      service, args[aa], imports));
+                    checkedAdd(listeners, new ServiceListener(
+                                   service, args[aa], imports));
                 }
             }
             methods.add(new ServiceMethod(service, m, imports));
diff --git a/src/java/com/threerings/presents/tools/InvocationTask.java b/src/java/com/threerings/presents/tools/InvocationTask.java
index 11b60bab6..3dbc2aae2 100644
--- a/src/java/com/threerings/presents/tools/InvocationTask.java
+++ b/src/java/com/threerings/presents/tools/InvocationTask.java
@@ -13,6 +13,7 @@ import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.Iterator;
+import java.util.List;
 
 import java.util.regex.Pattern;
 import java.util.regex.Matcher;
@@ -353,7 +354,7 @@ public abstract class InvocationTask extends Task
         FileUtils.writeStringToFile(new File(path), data, "UTF-8");
     }
 
-    protected static void checkedAdd (SortableArrayList list, String value)
+    protected static void checkedAdd (List list, Object value)
     {
         if (!list.contains(value)) {
             list.add(value);