diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/Def.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/Def.java
index 158086ab429..c24261dc5ac 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/Def.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/Def.java
@@ -138,7 +138,7 @@ public final class Def {
 
     /** Hack to rethrow unknown Exceptions from {@link MethodHandle#invokeExact}: */
     @SuppressWarnings("unchecked")
-    private static <T extends Throwable> void rethrow(Throwable t) throws T {
+    static <T extends Throwable> void rethrow(Throwable t) throws T {
         throw (T) t;
     }
     
diff --git a/modules/lang-painless/src/main/java/org/elasticsearch/painless/DefBootstrap.java b/modules/lang-painless/src/main/java/org/elasticsearch/painless/DefBootstrap.java
index 181aa10061f..f1651b5c869 100644
--- a/modules/lang-painless/src/main/java/org/elasticsearch/painless/DefBootstrap.java
+++ b/modules/lang-painless/src/main/java/org/elasticsearch/painless/DefBootstrap.java
@@ -158,11 +158,12 @@ public final class DefBootstrap {
                 final ClassValue<MethodHandle> megamorphicCache = new ClassValue<MethodHandle>() {
                     @Override
                     protected MethodHandle computeValue(Class<?> receiverType) {
+                        // it's too stupid that we cannot throw checked exceptions... (use rethrow puzzler):
                         try {
                             return lookup(flavor, name, receiverType, callArgs).asType(type);
-                        } catch (Throwable e) {
-                            // XXX: fix that
-                            throw new RuntimeException(e);
+                        } catch (Throwable t) {
+                            Def.rethrow(t);
+                            throw new AssertionError();
                         }
                     }
                 };