Index: RubyExecutionContext.cs
===================================================================
--- RubyExecutionContext.cs	(revision 94)
+++ RubyExecutionContext.cs	(working copy)
@@ -301,7 +301,9 @@
             MutableString version = new MutableString(RubyContext.MriVersion);
             MutableString platform = new MutableString("i386-mswin32");   // TODO: make this the correct string for MAC OS X in Silverlight
             MutableString releaseDate = new MutableString(RubyContext.MriReleaseDate);
+            MutableString rubyEngine = new MutableString("ironruby");
 
+            _objectClass.SetConstant("RUBY_ENGINE", rubyEngine);
             _objectClass.SetConstant("RUBY_VERSION", version);
             _objectClass.SetConstant("RUBY_PLATFORM", platform);
             _objectClass.SetConstant("RUBY_RELEASE_DATE", releaseDate);