diff --git a/src/java/org/apache/commons/collections/TreeBag.java b/src/java/org/apache/commons/collections/TreeBag.java
index 098d51bd7..f591eb2db 100644
--- a/src/java/org/apache/commons/collections/TreeBag.java
+++ b/src/java/org/apache/commons/collections/TreeBag.java
@@ -62,6 +62,14 @@ public class TreeBag extends DefaultMapBag implements SortedBag {
         addAll(coll);
     }
 
+    public boolean add(Object o) {
+        if(comparator() == null && !(o instanceof Comparable)) {
+            throw new IllegalArgumentException("Objects of type " + o.getClass() + " cannot be added to " + 
+                                               "a naturally ordered TreeBag as it does not implement Comparable");
+        }
+        return super.add(o);
+    }
+
     public Object first() {
         return ((SortedMap) getMap()).firstKey();
     }
diff --git a/src/java/org/apache/commons/collections/bag/TreeBag.java b/src/java/org/apache/commons/collections/bag/TreeBag.java
index 6c4ca968d..7191d6d3e 100644
--- a/src/java/org/apache/commons/collections/bag/TreeBag.java
+++ b/src/java/org/apache/commons/collections/bag/TreeBag.java
@@ -80,6 +80,15 @@ public class TreeBag
         addAll(coll);
     }
 
+    //-----------------------------------------------------------------------
+    public boolean add(Object o) {
+        if(comparator() == null && !(o instanceof Comparable)) {
+            throw new IllegalArgumentException("Objects of type " + o.getClass() + " cannot be added to " + 
+                                               "a naturally ordered TreeBag as it does not implement Comparable");
+        }
+        return super.add(o);
+    }
+
     //-----------------------------------------------------------------------
     public Object first() {
         return ((SortedMap) getMap()).firstKey();
diff --git a/src/test/org/apache/commons/collections/TestTreeBag.java b/src/test/org/apache/commons/collections/TestTreeBag.java
index 59d83fb70..5dcd5e60d 100644
--- a/src/test/org/apache/commons/collections/TestTreeBag.java
+++ b/src/test/org/apache/commons/collections/TestTreeBag.java
@@ -70,4 +70,15 @@ public class TestTreeBag extends AbstractTestBag {
       assertEquals("Should get last key",
                    "D", ((SortedBag)bag).last());
    }
+
+   public void testCollections265() {
+       Bag bag = new TreeBag();
+       try {
+           bag.add(new Object());
+           fail("IllegalArgumentException expected");
+       } catch(IllegalArgumentException iae) {
+           // expected;
+       }
+   }
+   
 }
diff --git a/src/test/org/apache/commons/collections/bag/TestTreeBag.java b/src/test/org/apache/commons/collections/bag/TestTreeBag.java
index 6a9e04290..7df16dc2e 100644
--- a/src/test/org/apache/commons/collections/bag/TestTreeBag.java
+++ b/src/test/org/apache/commons/collections/bag/TestTreeBag.java
@@ -71,6 +71,16 @@ public class TestTreeBag extends AbstractTestBag {
       assertEquals("Should get last key",
                    "D", ((SortedBag)bag).last());
    }
+
+   public void testCollections265() {
+       Bag bag = new TreeBag();
+       try {
+           bag.add(new Object());
+           fail("IllegalArgumentException expected");
+       } catch(IllegalArgumentException iae) {
+           // expected;
+       }
+   }
    
    public String getCompatibilityVersion() {
        return "3";