diff --git a/sphinx/domains/c.py b/sphinx/domains/c.py
index 4dc2f22cf..af2e5f8d9 100644
--- a/sphinx/domains/c.py
+++ b/sphinx/domains/c.py
@@ -3456,9 +3456,9 @@ class AliasNode(nodes.Element):
             assert parentKey is not None
             self.parentKey = parentKey
 
-    def copy(self: T) -> T:
+    def copy(self) -> 'AliasNode':
         return self.__class__(self.sig, self.maxdepth, self.document,
-                              env=None, parentKey=self.parentKey)  # type: ignore
+                              env=None, parentKey=self.parentKey)
 
 
 class AliasTransform(SphinxTransform):