diff --git a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
index 2d9f6eef35..7a0c6e6067 100644
--- a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
+++ b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.cpp
@@ -58,7 +58,7 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(GlobalObject& global_object,
         m_this_mode = ThisMode::Global;
 
     // 15.1.3 Static Semantics: IsSimpleParameterList, https://tc39.es/ecma262/#sec-static-semantics-issimpleparameterlist
-    set_has_simple_parameter_list(all_of(m_formal_parameters, [&](auto& parameter) {
+    m_has_simple_parameter_list = all_of(m_formal_parameters, [&](auto& parameter) {
         if (parameter.is_rest)
             return false;
         if (parameter.default_value)
@@ -66,7 +66,7 @@ ECMAScriptFunctionObject::ECMAScriptFunctionObject(GlobalObject& global_object,
         if (!parameter.binding.template has<FlyString>())
             return false;
         return true;
-    }));
+    });
 }
 
 void ECMAScriptFunctionObject::initialize(GlobalObject& global_object)
diff --git a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
index a620e67aa7..efca06b076 100644
--- a/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
+++ b/Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h
@@ -68,6 +68,9 @@ public:
     Vector<InstanceField> const& fields() const { return m_fields; }
     void add_field(StringOrSymbol property_key, ECMAScriptFunctionObject* initializer) { m_fields.empend(property_key, initializer); }
 
+    // This is for IsSimpleParameterList (static semantics)
+    bool has_simple_parameter_list() const { return m_has_simple_parameter_list; }
+
 protected:
     virtual bool is_strict_mode() const final { return m_strict; }
 
@@ -95,6 +98,7 @@ private:
     i32 m_function_length { 0 };
     FunctionKind m_kind { FunctionKind::Regular };
     bool m_is_arrow_function { false };
+    bool m_has_simple_parameter_list { false };
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/FunctionObject.h b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
index ca41124d64..ec8bedf665 100644
--- a/Userland/Libraries/LibJS/Runtime/FunctionObject.h
+++ b/Userland/Libraries/LibJS/Runtime/FunctionObject.h
@@ -39,22 +39,16 @@ public:
     // [[Realm]]
     virtual Realm* realm() const { return nullptr; }
 
-    // This is for IsSimpleParameterList (static semantics)
-    bool has_simple_parameter_list() const { return m_has_simple_parameter_list; }
-
 protected:
     virtual void visit_edges(Visitor&) override;
 
     explicit FunctionObject(Object& prototype);
     FunctionObject(Value bound_this, Vector<Value> bound_arguments, Object& prototype);
 
-    void set_has_simple_parameter_list(bool b) { m_has_simple_parameter_list = b; }
-
 private:
     virtual bool is_function() const override { return true; }
     Value m_bound_this;
     Vector<Value> m_bound_arguments;
-    bool m_has_simple_parameter_list { false };
 };
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/VM.cpp b/Userland/Libraries/LibJS/Runtime/VM.cpp
index 4622e60859..08ae93bbb3 100644
--- a/Userland/Libraries/LibJS/Runtime/VM.cpp
+++ b/Userland/Libraries/LibJS/Runtime/VM.cpp
@@ -374,7 +374,7 @@ Value VM::get_variable(const FlyString& name, GlobalObject& global_object)
             if (possible_match.has_value())
                 return possible_match.value().value;
             if (!context.arguments_object) {
-                if (context.function->is_strict_mode() || !context.function->has_simple_parameter_list()) {
+                if (context.function->is_strict_mode() || (is<ECMAScriptFunctionObject>(context.function) && !static_cast<ECMAScriptFunctionObject*>(context.function)->has_simple_parameter_list())) {
                     context.arguments_object = create_unmapped_arguments_object(global_object, context.arguments.span());
                 } else {
                     context.arguments_object = create_mapped_arguments_object(global_object, *context.function, verify_cast<ECMAScriptFunctionObject>(context.function)->formal_parameters(), context.arguments.span(), *lexical_environment());