diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index 172d44555b94..1c85e33b8cc9 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -2054,7 +2054,17 @@ def infer_arg_types_in_context(
                 # cases. A cleaner alternative would be to switch to single bin type
                 # inference, but this is a lot of work.
                 old = self.infer_more_unions_for_recursive_type(ctx)
-                res.append(self.accept(arg, ctx))
+                arg_type = self.accept(arg, ctx)
+                proper_ctx = get_proper_type(ctx)
+                proper_arg_type = get_proper_type(arg_type)
+                if (
+                    isinstance(proper_ctx, TypeVarType)
+                    and isinstance(proper_arg_type, Instance)
+                    and proper_arg_type.last_known_value is not None
+                    and proper_arg_type.last_known_value.is_sentinel_literal()
+                ):
+                    arg_type = proper_arg_type.last_known_value
+                res.append(arg_type)
                 # We need to manually restore union inference state, ugh.
                 type_state.infer_unions = old
             else:
diff --git a/test-data/unit/check-sentinels.test b/test-data/unit/check-sentinels.test
index 6d39c11375bb..6a4172b6c7b3 100644
--- a/test-data/unit/check-sentinels.test
+++ b/test-data/unit/check-sentinels.test
@@ -189,3 +189,13 @@ def func(x: int | MISSING = MISSING) -> None:
 func(MISSING)
 func(ALIAS)  # E: Argument 1 to "func" has incompatible type "Sentinel"; expected "int | MISSING"
 [builtins fixtures/tuple.pyi]
+
+[case testDictGetPEP661SentinelDefault]
+from typing_extensions import assert_type, sentinel
+
+Unknown = sentinel("Unknown")
+
+def func(d: dict[str, str]) -> None:
+    var = d.get("key", Unknown)
+    assert_type(var, str | Unknown)
+[builtins fixtures/dict.pyi]