--- a/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/impl/DefaultTruffleRuntime.java	Fri Jan 24 18:34:18 2014 +0100
+++ b/graal/com.oracle.truffle.api/src/com/oracle/truffle/api/impl/DefaultTruffleRuntime.java	Fri Jan 24 18:13:38 2014 -0800
@@ -31,16 +31,25 @@
 /**
  * Default implementation of the Truffle runtime if the virtual machine does not provide a better
  * performing alternative.
+ * <p>
+ * This is an implementation-specific class. Do not use or instantiate it. Instead, use
+ * {@link Truffle#getRuntime()} to retrieve the current {@link TruffleRuntime}.
  */
 public final class DefaultTruffleRuntime implements TruffleRuntime {
 
+    public DefaultTruffleRuntime() {
+        if (Truffle.getRuntime() != null) {
+            throw new IllegalArgumentException("Cannot instantiate DefaultTruffleRuntime. Use Truffle.getRuntime() instead.");
+        }
+    }
+
     @Override
     public String getName() {
         return "Default Truffle Runtime";
     }
 
     @Override
-    public CallTarget createCallTarget(RootNode rootNode) {
+    public RootCallTarget createCallTarget(RootNode rootNode) {
         return new DefaultCallTarget(rootNode);
     }