diff --git a/js/rhino/org/mozilla/javascript/NativeGlobal.java b/js/rhino/org/mozilla/javascript/NativeGlobal.java
index 9c3f1d68459..02a1cd9fe61 100644
--- a/js/rhino/org/mozilla/javascript/NativeGlobal.java
+++ b/js/rhino/org/mozilla/javascript/NativeGlobal.java
@@ -79,7 +79,8 @@ public class NativeGlobal {
         global.defineProperty("undefined", Undefined.instance,
                               ScriptableObject.DONTENUM);
 
-        String[] errorMethods = { "EvalError",  
+        String[] errorMethods = { "ConversionError",
+                                  "EvalError",  
                                   "RangeError",
                                   "ReferenceError",
                                   "SyntaxError",
diff --git a/js/rhino/org/mozilla/javascript/ScriptRuntime.java b/js/rhino/org/mozilla/javascript/ScriptRuntime.java
index 68d9307cc8b..2357a156faa 100644
--- a/js/rhino/org/mozilla/javascript/ScriptRuntime.java
+++ b/js/rhino/org/mozilla/javascript/ScriptRuntime.java
@@ -766,10 +766,12 @@ public class ScriptRuntime {
         catch (ClassCastException e) {
             start = toObject(scope, obj);
         }
-        if (start == null) {
+        if (start == null || start == Undefined.instance) {
+            String msg = start == null ? "msg.null.to.object" 
+                                       : "msg.undefined";
             throw NativeGlobal.constructError(
-                        Context.getContext(), "TypeError",
-                        ScriptRuntime.getMessage("msg.null.to.object", null),
+                        Context.getContext(), "ConversionError",
+                        ScriptRuntime.getMessage(msg, null),
                         scope);
         }
         Scriptable m = start;
diff --git a/js/rhino/src/org/mozilla/javascript/NativeGlobal.java b/js/rhino/src/org/mozilla/javascript/NativeGlobal.java
index 9c3f1d68459..02a1cd9fe61 100644
--- a/js/rhino/src/org/mozilla/javascript/NativeGlobal.java
+++ b/js/rhino/src/org/mozilla/javascript/NativeGlobal.java
@@ -79,7 +79,8 @@ public class NativeGlobal {
         global.defineProperty("undefined", Undefined.instance,
                               ScriptableObject.DONTENUM);
 
-        String[] errorMethods = { "EvalError",  
+        String[] errorMethods = { "ConversionError",
+                                  "EvalError",  
                                   "RangeError",
                                   "ReferenceError",
                                   "SyntaxError",
diff --git a/js/rhino/src/org/mozilla/javascript/ScriptRuntime.java b/js/rhino/src/org/mozilla/javascript/ScriptRuntime.java
index 68d9307cc8b..2357a156faa 100644
--- a/js/rhino/src/org/mozilla/javascript/ScriptRuntime.java
+++ b/js/rhino/src/org/mozilla/javascript/ScriptRuntime.java
@@ -766,10 +766,12 @@ public class ScriptRuntime {
         catch (ClassCastException e) {
             start = toObject(scope, obj);
         }
-        if (start == null) {
+        if (start == null || start == Undefined.instance) {
+            String msg = start == null ? "msg.null.to.object" 
+                                       : "msg.undefined";
             throw NativeGlobal.constructError(
-                        Context.getContext(), "TypeError",
-                        ScriptRuntime.getMessage("msg.null.to.object", null),
+                        Context.getContext(), "ConversionError",
+                        ScriptRuntime.getMessage(msg, null),
                         scope);
         }
         Scriptable m = start;