| Index: runtime/lib/double.dart | 
| diff --git a/runtime/lib/double.dart b/runtime/lib/double.dart | 
| index f4025f3b745ed90d6c66233c91568357720d57a6..aee84e23bc74334e383864da1cc1359eb2bb1d1f 100644 | 
| --- a/runtime/lib/double.dart | 
| +++ b/runtime/lib/double.dart | 
| @@ -114,7 +114,9 @@ class _Double implements double { | 
| if (exponent == 0) { | 
| return 1.0;  // ECMA-262 15.8.2.13 | 
| } | 
| -    // Throw NullPointerException if exponent is null. | 
| +    if (exponent is! num) { | 
| +      throw new ArgumentError(null); | 
| +    } | 
| double doubleExponent = exponent.toDouble(); | 
| if (isNaN || exponent.isNaN) { | 
| return double.NAN; | 
|  |