diff --git a/openfeature/client.py b/openfeature/client.py
index 8adedf9b..84ae35ac 100644
--- a/openfeature/client.py
+++ b/openfeature/client.py
@@ -890,7 +890,7 @@ async def _create_provider_evaluation_async(
         if err := _typecheck_flag_value(value=resolution.value, flag_type=flag_type):
             return FlagEvaluationDetails(
                 flag_key=flag_key,
-                value=resolution.value,
+                value=default_value,
                 reason=Reason.ERROR,
                 error_code=err.error_code,
                 error_message=err.error_message,
@@ -1001,6 +1001,9 @@ def _typecheck_flag_value(
     py_type = type_map.get(flag_type)
     if not py_type:
         return GeneralError(error_message="Unknown flag type")
-    if not isinstance(value, py_type):
+    # bool subclasses int, but booleans are not integer flag values.
+    if not isinstance(value, py_type) or (
+        flag_type == FlagType.INTEGER and isinstance(value, bool)
+    ):
         return TypeMismatchError(f"Expected type {py_type} but got {type(value)}")
     return None
diff --git a/tests/test_client.py b/tests/test_client.py
index 64598936..97d2e49b 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -434,6 +434,123 @@ async def test_typecheck_flag_value_general_error():
     assert err.error_message == "Unknown flag type"
 
 
+@pytest.mark.parametrize(
+    "flag_type, flag_value, default_value",
+    [
+        ("integer", True, 1),
+        ("integer", False, 0),
+        ("float", True, 1.0),
+        ("float", False, 0.0),
+        ("boolean", 1, False),
+        ("integer", "1", 0),
+        ("float", 1, 0.0),
+        ("string", True, "fallback"),
+        ("object", True, {}),
+    ],
+)
+@pytest.mark.parametrize("is_async", [False, True], ids=["sync", "async"])
+@pytest.mark.asyncio
+async def test_client_returns_default_on_type_mismatch(
+    flag_type, flag_value, default_value, is_async
+):
+    provider = InMemoryProvider(
+        {"flag": InMemoryFlag("enabled", {"enabled": flag_value})}
+    )
+    api.set_provider_and_wait(provider)
+    client = get_client()
+    spy_hook = MagicMock(spec=Hook)
+    client.add_hooks([spy_hook])
+    suffix = "_async" if is_async else ""
+
+    get_details = getattr(client, f"get_{flag_type}_details{suffix}")
+    details = get_details("flag", default_value)
+    if is_async:
+        details = await details
+
+    assert details.flag_key == "flag"
+    assert details.value == default_value
+    # Equality alone cannot distinguish True from 1 (or False from 0).
+    assert type(details.value) is type(default_value)
+    assert details.reason == Reason.ERROR
+    assert details.error_code == ErrorCode.TYPE_MISMATCH
+    expected_type = (dict, list) if flag_type == "object" else type(default_value)
+    assert (
+        details.error_message
+        == f"Expected type {expected_type} but got {type(flag_value)}"
+    )
+    spy_hook.error.assert_called_once()
+    assert (
+        spy_hook.error.call_args.kwargs["exception"].error_code
+        == ErrorCode.TYPE_MISMATCH
+    )
+    spy_hook.after.assert_not_called()
+    spy_hook.finally_after.assert_called_once()
+    assert spy_hook.finally_after.call_args.kwargs["details"].value == default_value
+    assert type(spy_hook.finally_after.call_args.kwargs["details"].value) is type(
+        default_value
+    )
+
+    get_value = getattr(client, f"get_{flag_type}_value{suffix}")
+    value = get_value("flag", default_value)
+    if is_async:
+        value = await value
+    assert value == default_value
+    assert type(value) is type(default_value)
+
+
+@pytest.mark.parametrize(
+    "flag_type, flag_value, default_value",
+    [
+        ("boolean", True, False),
+        ("boolean", False, True),
+        ("integer", 0, -1),
+        ("integer", 1, -1),
+        ("integer", -1, 0),
+        ("float", 0.0, -1.0),
+        ("float", 1.5, -1.0),
+        ("string", "enabled", "default"),
+        ("object", {"enabled": True}, {}),
+        ("object", [True, 1, "enabled"], []),
+    ],
+)
+@pytest.mark.parametrize("is_async", [False, True], ids=["sync", "async"])
+@pytest.mark.asyncio
+async def test_client_preserves_matching_flag_types(
+    flag_type, flag_value, default_value, is_async
+):
+    provider = InMemoryProvider(
+        {"flag": InMemoryFlag("enabled", {"enabled": flag_value})}
+    )
+    api.set_provider_and_wait(provider)
+    client = get_client()
+    suffix = "_async" if is_async else ""
+
+    get_details = getattr(client, f"get_{flag_type}_details{suffix}")
+    details = get_details("flag", default_value)
+    if is_async:
+        details = await details
+
+    assert details.value == flag_value
+    assert type(details.value) is type(flag_value)
+    assert details.variant == "enabled"
+    assert details.reason == Reason.STATIC
+    assert details.error_code is None
+
+    get_value = getattr(client, f"get_{flag_type}_value{suffix}")
+    value = get_value("flag", default_value)
+    if is_async:
+        value = await value
+    assert value == flag_value
+    assert type(value) is type(flag_value)
+
+
+def test_typecheck_flag_value_accepts_integer_subclasses():
+    class IntegerValue(int):
+        pass
+
+    assert _typecheck_flag_value(IntegerValue(1), FlagType.INTEGER) is None
+
+
 @pytest.mark.asyncio
 async def test_typecheck_flag_value_type_mismatch_error():
     # Given