diff --git a/astroid/nodes/node_classes.py b/astroid/nodes/node_classes.py
index 56921d2d30..d233ff0360 100644
--- a/astroid/nodes/node_classes.py
+++ b/astroid/nodes/node_classes.py
@@ -689,6 +689,7 @@ def fromlineno(self) -> int:
         Can also return 0 if the line can not be determined.
         """
         lineno = super().fromlineno
+        assert self.parent is not None
         return max(lineno, self.parent.fromlineno or 0)
 
     @cached_property