src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.options.processor/src/org/graalvm/compiler/options/processor/OptionProcessor.java

@@ -172,11 +172,11 @@
                 processingEnv.getMessager().printMessage(Kind.ERROR, "Unexpected enclosing element kind: " + enclosing.getKind(), element);
                 return;
             }
             enclosing = enclosing.getEnclosingElement();
         }
-        if (enclosingPackage == null) {
+        if (enclosingPackage == null || enclosingPackage.isUnnamed()) {
             processingEnv.getMessager().printMessage(Kind.ERROR, "Option field cannot be declared in the unnamed package", element);
             return;
         }
         List<String> helpValue = getAnnotationValueList(annotation, "help", String.class);
         String help = "";