diff --git a/src/UserData/UserDataScriptType.hpp b/src/UserData/UserDataScriptType.hpp
index 45cd35b..d7ba5f0 100644
--- a/src/UserData/UserDataScriptType.hpp
+++ b/src/UserData/UserDataScriptType.hpp
@@ -84,6 +84,8 @@ namespace Porygon::UserData {
             if (!ud->ContainsField(hash.GetHash()))
                 return false;
             auto field = _userData->Get()->GetField(hash.GetHash());
+            if (!field->HasSetter())
+                return false;
             return (val->CastableTo(field->GetType(), false) != CastResult::InvalidCast);
 
         }
@@ -93,6 +95,8 @@ namespace Porygon::UserData {
             if (!ud->ContainsField(indexer.GetHash()))
                 return false;
             auto field = _userData->Get()->GetField(indexer.GetHash());
+            if (!field->HasSetter())
+                return false;
             return (val->CastableTo(field->GetType(), false) != CastResult::InvalidCast);
         }