diff --git a/vm/src/builtins/mappingproxy.rs b/vm/src/builtins/mappingproxy.rs
index e5df6bac7..a650fffd2 100644
--- a/vm/src/builtins/mappingproxy.rs
+++ b/vm/src/builtins/mappingproxy.rs
@@ -37,7 +37,7 @@ impl Constructor for PyMappingProxy {
     type Args = PyObjectRef;
 
     fn py_new(cls: PyTypeRef, mapping: Self::Args, vm: &VirtualMachine) -> PyResult {
-        if !PyMapping::from(mapping.as_ref()).has_protocol(vm)
+        if !PyMapping::from(mapping.as_ref()).check(vm)
             || mapping.payload_if_subclass::<PyList>(vm).is_some()
             || mapping.payload_if_subclass::<PyTuple>(vm).is_some()
         {
diff --git a/vm/src/protocol/mapping.rs b/vm/src/protocol/mapping.rs
index 44e3e631a..da2fb020e 100644
--- a/vm/src/protocol/mapping.rs
+++ b/vm/src/protocol/mapping.rs
@@ -50,7 +50,7 @@ impl<'a> PyMapping<'a> {
 
     pub fn try_protocol(obj: &'a PyObject, vm: &VirtualMachine) -> PyResult<Self> {
         let zelf = Self::from(obj);
-        if zelf.has_protocol(vm) {
+        if zelf.check(vm) {
             Ok(zelf)
         } else {
             Err(vm.new_type_error(format!("{} is not a mapping object", zelf.obj.class())))
@@ -60,7 +60,7 @@ impl<'a> PyMapping<'a> {
 
 impl PyMapping<'_> {
     // PyMapping::Check
-    pub fn has_protocol(&self, vm: &VirtualMachine) -> bool {
+    pub fn check(&self, vm: &VirtualMachine) -> bool {
         self.methods(vm).subscript.is_some()
     }
 
diff --git a/vm/src/protocol/object.rs b/vm/src/protocol/object.rs
index b48f68b64..148abe09b 100644
--- a/vm/src/protocol/object.rs
+++ b/vm/src/protocol/object.rs
@@ -464,8 +464,9 @@ impl PyObject {
 
         let needle = needle.into_pyobject(vm);
 
-        if let Ok(mapping) = PyMapping::try_protocol(self, vm) {
-            mapping.ass_subscript(&needle, Some(value), vm)
+        let mapping = PyMapping::from(self);
+        if let Some(f) = mapping.methods(vm).ass_subscript {
+            f(&mapping, &needle, Some(value), vm)
         } else {
             // TODO: sequence protocol
             vm.get_special_method(self.to_owned(), "__setitem__")?
@@ -491,8 +492,9 @@ impl PyObject {
 
         let needle = needle.into_pyobject(vm);
 
-        if let Ok(mapping) = PyMapping::try_protocol(self, vm) {
-            mapping.ass_subscript(&needle, None, vm)
+        let mapping = PyMapping::from(self);
+        if let Some(f) = mapping.methods(vm).ass_subscript {
+            f(&mapping, &needle, None, vm)
         } else {
             //TODO: sequence protocol
             vm.get_special_method(self.to_owned(), "__delitem__")?