src/java.base/share/classes/jdk/internal/loader/BuiltinClassLoader.java

@@ -90,11 +90,12 @@
 public class BuiltinClassLoader
     extends SecureClassLoader
 {
     static {
         if (!ClassLoader.registerAsParallelCapable())
-            throw new InternalError();
+            throw new InternalError("Classloader is not registered" + 
+                " as parallel capable.");
     }
 
     // parent ClassLoader
     private final BuiltinClassLoader parent;