diff --git a/vm/src/builtins/union.rs b/vm/src/builtins/union.rs
index 996d3f66543..b8e34a7268f 100644
--- a/vm/src/builtins/union.rs
+++ b/vm/src/builtins/union.rs
@@ -40,6 +40,12 @@ impl PyUnion {
         Self { args, parameters }
     }
 
+    /// Direct access to args field, matching CPython's _Py_union_args
+    #[inline]
+    pub fn args(&self) -> &PyTupleRef {
+        &self.args
+    }
+
     fn repr(&self, vm: &VirtualMachine) -> PyResult<String> {
         fn repr_item(obj: PyObjectRef, vm: &VirtualMachine) -> PyResult<String> {
             if obj.is(vm.ctx.types.none_type) {
diff --git a/vm/src/protocol/object.rs b/vm/src/protocol/object.rs
index 61973def4b4..98046bab820 100644
--- a/vm/src/protocol/object.rs
+++ b/vm/src/protocol/object.rs
@@ -497,30 +497,31 @@ impl PyObject {
     /// via the __subclasscheck__ magic method.
     /// PyObject_IsSubclass/object_issubclass
     pub fn is_subclass(&self, cls: &PyObject, vm: &VirtualMachine) -> PyResult<bool> {
+        let derived = self;
         // PyType_CheckExact(cls)
         if cls.class().is(vm.ctx.types.type_type) {
-            if self.is(cls) {
+            if derived.is(cls) {
                 return Ok(true);
             }
-            return self.recursive_issubclass(cls, vm);
+            return derived.recursive_issubclass(cls, vm);
         }
 
         // Check for Union type - CPython handles this before tuple
-        let cls_to_check = if cls.class().is(vm.ctx.types.union_type) {
+        let cls = if cls.class().is(vm.ctx.types.union_type) {
             // Get the __args__ attribute which contains the union members
-            if let Ok(args) = cls.get_attr(identifier!(vm, __args__), vm) {
-                args
-            } else {
-                cls.to_owned()
-            }
+            // Match CPython's _Py_union_args which directly accesses the args field
+            let union = cls
+                .downcast_ref::<crate::builtins::PyUnion>()
+                .expect("union is already checked");
+            union.args().as_object()
         } else {
-            cls.to_owned()
+            cls
         };
 
-        // Check if cls_to_check is a tuple
-        if let Ok(tuple) = cls_to_check.try_to_value::<&Py<PyTuple>>(vm) {
-            for typ in tuple {
-                if vm.with_recursion("in __subclasscheck__", || self.is_subclass(typ, vm))? {
+        // Check if cls is a tuple
+        if let Some(tuple) = cls.downcast_ref::<PyTuple>() {
+            for item in tuple {
+                if vm.with_recursion("in __subclasscheck__", || derived.is_subclass(item, vm))? {
                     return Ok(true);
                 }
             }
@@ -528,14 +529,14 @@ impl PyObject {
         }
 
         // Check for __subclasscheck__ method
-        if let Some(meth) = vm.get_special_method(cls, identifier!(vm, __subclasscheck__))? {
-            let ret = vm.with_recursion("in __subclasscheck__", || {
-                meth.invoke((self.to_owned(),), vm)
+        if let Some(checker) = vm.get_special_method(cls, identifier!(vm, __subclasscheck__))? {
+            let res = vm.with_recursion("in __subclasscheck__", || {
+                checker.invoke((derived.to_owned(),), vm)
             })?;
-            return ret.try_to_bool(vm);
+            return res.try_to_bool(vm);
         }
 
-        self.recursive_issubclass(cls, vm)
+        derived.recursive_issubclass(cls, vm)
     }
 
     /// Real isinstance check without going through __instancecheck__
@@ -601,16 +602,14 @@ impl PyObject {
 
         // Check for Union type (e.g., int | str) - CPython checks this before tuple
         if cls.class().is(vm.ctx.types.union_type) {
-            if let Ok(args) = cls.get_attr(identifier!(vm, __args__), vm) {
-                if let Ok(tuple) = args.try_to_ref::<PyTuple>(vm) {
-                    for typ in tuple {
-                        if vm
-                            .with_recursion("in __instancecheck__", || self.is_instance(typ, vm))?
-                        {
-                            return Ok(true);
-                        }
-                    }
-                    return Ok(false);
+            // Match CPython's _Py_union_args which directly accesses the args field
+            let union = cls
+                .try_to_ref::<crate::builtins::PyUnion>(vm)
+                .expect("checked by is");
+            let tuple = union.args();
+            for typ in tuple.iter() {
+                if vm.with_recursion("in __instancecheck__", || self.is_instance(typ, vm))? {
+                    return Ok(true);
                 }
             }
         }