python
diff --git a/‎mypy/semanal.py‎
Lines changed: 11 additions & 0 deletions b/‎mypy/semanal.py‎
Lines changed: 11 additions & 0 deletions
diff --git a/‎test-data/unit/check-classes.test‎
Lines changed: 14 additions & 0 deletions b/‎test-data/unit/check-classes.test‎
Lines changed: 14 additions & 0 deletions
@@ -4782,6 +4782,10 @@ def analyze_member_lvalue(
                     self.type.names[lval.name] = SymbolTableNode(MDEF, v, implicit=True)
                     for func in self.scope.functions:
                         func.def_or_infer_vars = True
+
+        if self.is_self_member_ref(lval) or self.is_cls_member_ref(lval):
+            assert self.type, "Self or cls member outside a class"
+            cur_node = self.type.names.get(lval.name)
             if (
                 cur_node
                 and isinstance(cur_node.node, Var)
@@ -4799,6 +4803,13 @@ def is_self_member_ref(self, memberexpr: MemberExpr) -> bool:
         node = memberexpr.expr.node
         return isinstance(node, Var) and node.is_self
 
+    def is_cls_member_ref(self, memberexpr: MemberExpr) -> bool:
+        """Does memberexpr to refer to an attribute of cls?"""
+        if not isinstance(memberexpr.expr, NameExpr):
+            return False
+        node = memberexpr.expr.node
+        return isinstance(node, Var) and node.is_cls
+
     def check_lvalue_validity(self, node: Expression | SymbolNode | None, ctx: Context) -> None:
         if isinstance(node, TypeVarExpr):
             self.fail("Invalid assignment target", ctx)
 
@@ -9727,3 +9727,17 @@ def f() -> None:
     class X:
         ...
     undefined  # E: Name "undefined" is not defined
+
+[case testPartialNoneTypeClassMethod]
+# flags: --local-partial-types
+
+class C:
+    x = None
+
+    @classmethod
+    def foo(cls) -> None:
+        if not cls.x:
+            cls.x = 1
+
+reveal_type(C.x)  # N: Revealed type is "builtins.int | None"
+[builtins fixtures/classmethod.pyi]