diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 754ba6f093f5..38b5c2419d95 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -2950,7 +2950,7 @@ def visit_comparison_expr(self, e: ComparisonExpr) -> Type:
                 right_type = get_proper_type(right_type)
                 item_types: Sequence[Type] = [right_type]
                 if isinstance(right_type, UnionType):
-                    item_types = list(right_type.items)
+                    item_types = list(right_type.relevant_items())
 
                 sub_result = self.bool_type()
 
diff --git a/test-data/unit/check-optional.test b/test-data/unit/check-optional.test
index db07290f7b40..754c6b52ff19 100644
--- a/test-data/unit/check-optional.test
+++ b/test-data/unit/check-optional.test
@@ -1031,3 +1031,12 @@ def f1(b: bool) -> Optional[int]:
 class Defer:
     def __init__(self) -> None:
         self.defer = 10
+
+[case testOptionalIterator]
+# mypy: no-strict-optional
+from typing import Optional, List
+
+x: Optional[List[int]]
+if 3 in x:
+    pass
+