diff --git a/src/helma/scripting/rhino/MapWrapper.java b/src/helma/scripting/rhino/MapWrapper.java
index a1bfbf31..681f1edc 100644
--- a/src/helma/scripting/rhino/MapWrapper.java
+++ b/src/helma/scripting/rhino/MapWrapper.java
@@ -20,6 +20,7 @@ import org.mozilla.javascript.Context;
 import org.mozilla.javascript.Scriptable;
 import org.mozilla.javascript.ScriptableObject;
 import org.mozilla.javascript.Wrapper;
+import org.mozilla.javascript.Undefined;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -60,7 +61,9 @@ public class MapWrapper extends ScriptableObject {
             map = new HashMap();
         }
 
-        if (value instanceof Wrapper) {
+        if (value == null || value == Undefined.instance) {
+            map.remove(name);
+        } else if (value instanceof Wrapper) {
             map.put(name, ((Wrapper) value).unwrap());
         } else {
             map.put(name, value);
@@ -131,7 +134,10 @@ public class MapWrapper extends ScriptableObject {
         if (map == null) {
             map = new HashMap();
         }
-        if (value instanceof Wrapper) {
+
+        if (value == null || value == Undefined.instance) {
+            map.remove(Integer.toString(idx));
+        } else if (value instanceof Wrapper) {
             map.put(Integer.toString(idx), ((Wrapper) value).unwrap());
         } else {
             map.put(Integer.toString(idx), value);