diff --git a/mypy/semanal_shared.py b/mypy/semanal_shared.py
index bdd01ef6a6f3..e94604b66381 100644
--- a/mypy/semanal_shared.py
+++ b/mypy/semanal_shared.py
@@ -46,6 +46,7 @@
     TypeVarLikeType,
     TypeVarTupleType,
     UnpackType,
+    flatten_nested_tuples,
     get_proper_type,
 )
 
@@ -290,7 +291,7 @@ def calculate_tuple_fallback(typ: TupleType) -> None:
     fallback = typ.partial_fallback
     assert fallback.type.fullname == "builtins.tuple"
     items = []
-    for item in typ.items:
+    for item in flatten_nested_tuples(typ.items):
         # TODO: this duplicates some logic in typeops.tuple_fallback().
         if isinstance(item, UnpackType):
             unpacked_type = get_proper_type(item.type)
diff --git a/test-data/unit/check-typevar-tuple.test b/test-data/unit/check-typevar-tuple.test
index d364439f22e9..830c41a37706 100644
--- a/test-data/unit/check-typevar-tuple.test
+++ b/test-data/unit/check-typevar-tuple.test
@@ -2628,3 +2628,11 @@ def fn(f: Callable[[*tuple[T]], int]) -> Callable[[*tuple[T]], int]: ...
 def test(*args: Unpack[tuple[T]]) -> int: ...
 reveal_type(fn(test))  # N: Revealed type is "def [T] (T`1) -> builtins.int"
 [builtins fixtures/tuple.pyi]
+
+[case testNoCrashSubclassingTUpleWithTrivialUnpack]
+# https://github.com/python/mypy/issues/19105
+from typing import Unpack
+
+class A(tuple[Unpack[tuple[int]]]): ...
+class B(tuple[Unpack[tuple[()]]]): ...
+[builtins fixtures/tuple.pyi]