diff --git a/src/main/java/org/truffleruby/cext/CExtNodes.java b/src/main/java/org/truffleruby/cext/CExtNodes.java
index e12e45019a09..d66f0058c6c1 100644
--- a/src/main/java/org/truffleruby/cext/CExtNodes.java
+++ b/src/main/java/org/truffleruby/cext/CExtNodes.java
@@ -1887,6 +1887,7 @@ Object addToMarkList(Object guardedObject,
     }
 
     @CoreMethod(names = "set_mark_list_on_object", onSingleton = true, required = 1)
+    @ReportPolymorphism
     public abstract static class SetMarkList extends CoreMethodArrayArgumentsNode {
 
         @Specialization