diff --git a/lib/Sema/TypeCheckType.cpp b/lib/Sema/TypeCheckType.cpp
index 9341a7054726c..e63d335c6a0fa 100644
--- a/lib/Sema/TypeCheckType.cpp
+++ b/lib/Sema/TypeCheckType.cpp
@@ -4280,8 +4280,15 @@ NeverNullType TypeResolver::resolveASTFunctionType(
     if (!repr->isInvalid())
       isolation = FunctionTypeIsolation::forNonIsolated();
   } else if (!getWithoutClaiming<CallerIsolatedTypeRepr>(attrs)) {
-    if (ctx.LangOpts.getFeatureState(Feature::NonisolatedNonsendingByDefault)
-            .isEnabledForMigration()) {
+    // Infer async function type as `nonisolated(nonsending)` if there is
+    // no `@concurrent` or `nonisolated(nonsending)` attribute and isolation
+    // is nonisolated.
+    if (ctx.LangOpts.hasFeature(Feature::NonisolatedNonsendingByDefault) &&
+        repr->isAsync() && isolation.isNonIsolated()) {
+      isolation = FunctionTypeIsolation::forNonIsolatedCaller();
+    } else if (ctx.LangOpts
+                   .getFeatureState(Feature::NonisolatedNonsendingByDefault)
+                   .isEnabledForMigration()) {
       // Diagnose only in the interface stage, which is run once.
       if (inStage(TypeResolutionStage::Interface)) {
         warnAboutNewNonisolatedAsyncExecutionBehavior(ctx, repr, isolation);
diff --git a/test/Concurrency/attr_execution/attr_execution.swift b/test/Concurrency/attr_execution/attr_execution.swift
index be1118ecb4d56..93702c1c8aacb 100644
--- a/test/Concurrency/attr_execution/attr_execution.swift
+++ b/test/Concurrency/attr_execution/attr_execution.swift
@@ -14,3 +14,69 @@ func concurrentTest() async {}
 // CHECK: sil hidden [ossa] @$s14attr_execution10callerTestyyYaF : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> () {
 nonisolated(nonsending)
 func callerTest() async {}
+
+struct Test {
+  // CHECK-LABEL: // closure #1 in variable initialization expression of Test.x
+  // CHECK: // Isolation: caller_isolation_inheriting
+  // CHECK: sil private [ossa] @$s14attr_execution4TestV1xyyYaYCcvpfiyyYaYCcfU_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+  var x: () async -> Void = {}
+
+  // CHECK-LABEL: // Test.test()
+  // CHECK: // Isolation: caller_isolation_inheriting
+  // CHECK: sil hidden [ossa] @$s14attr_execution4TestV4testyyYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed Test) -> ()
+  // CHECK: bb0([[ISOLATION:%.*]] : @guaranteed $Optional<any Actor>, [[SELF:%.*]] : @guaranteed $Test)
+  // CHECK: [[X_REF:%.*]] = struct_extract %1, #Test.x
+  // CHECK: [[X_REF_COPY:%.]] = copy_value [[X_REF]]
+  // CHECK: [[BORROWED_X:%.*]] = begin_borrow [[X_REF_COPY]]
+  // CHECK: apply [[BORROWED_X]]([[ISOLATION]]) : $@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+  // CHECK: } // end sil function '$s14attr_execution4TestV4testyyYaF'
+  func test() async {
+    await x()
+  }
+
+  // CHECK-LABEL: // Test.testParam(fn:)
+  // CHECK: // Isolation: caller_isolation_inheriting
+  // CHECK: sil hidden [ossa] @$s14attr_execution4TestV9testParam2fnyyyYaYCcSg_tYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed Optional<@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()>, @guaranteed Test) -> ()
+  // CHECK: bb0([[ISOLATION:%.*]] : @guaranteed $Optional<any Actor>, [[OPT_FN:%.*]] : @guaranteed $Optional<@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()>, [[SELF:%.*]] : @guaranteed $Test)
+  // CHECK: bb1([[FN:%.*]] : @owned $@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ())
+  // CHECK: [[BORROWED_FN:%.*]] = begin_borrow [[FN]]
+  // CHECK: apply [[BORROWED_FN]]([[ISOLATION]]) : $@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()  
+  // CHECK: } // end sil function '$s14attr_execution4TestV9testParam2fnyyyYaYCcSg_tYaF'
+  func testParam(fn: (() async -> Void)?) async {
+    await fn?()
+  }
+}
+
+// CHECK-LABEL: // testLocal()
+// CHECK: // Isolation: caller_isolation_inheriting
+// CHECK: sil hidden [ossa] @$s14attr_execution9testLocalyyYaF : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> () {
+// CHECK: bb0([[ISOLATION:%.*]] : @guaranteed $Optional<any Actor>)
+// CHECK: bb1([[FN:%.*]] : @owned $@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ())
+// CHECK: [[BORROWED_FN:%.*]] = begin_borrow [[FN]]
+// CHECK: apply [[BORROWED_FN]]([[ISOLATION]]) : $@async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+// CHECK: } // end sil function '$s14attr_execution9testLocalyyYaF'
+func testLocal() async {
+  let fn: (() async -> Void)? = nil
+  await fn?()
+}
+
+// CHECK-LABEL: // takesClosure(fn:)
+// CHECK: // Isolation: unspecified
+// CHECK: sil hidden [ossa] @$s14attr_execution12takesClosure2fnyyyYaYCXE_tF : $@convention(thin) (@guaranteed @noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()) -> ()
+func takesClosure(fn: () async -> Void) {
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s14attr_execution11testClosureyyF : $@convention(thin) () -> ()
+// CHECK:  [[CLOSURE:%.*]] = function_ref @$s14attr_execution11testClosureyyFyyYaYCXEfU_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+// CHECK:  [[THUNKED_CLOSURE:%.*]] = thin_to_thick_function %0 to $@noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+// CHECK:  [[TAKES_CLOSURE:%.*]] = function_ref @$s14attr_execution12takesClosure2fnyyyYaYCXE_tF : $@convention(thin) (@guaranteed @noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()) -> ()
+// CHECK:  apply [[TAKES_CLOSURE]]([[THUNKED_CLOSURE]])
+// CHECK: } // end sil function '$s14attr_execution11testClosureyyF'
+
+// CHECK-LABEL: // closure #1 in testClosure()
+// CHECK: // Isolation: caller_isolation_inheriting
+// CHECK: sil private [ossa] @$s14attr_execution11testClosureyyFyyYaYCXEfU_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>) -> ()
+func testClosure() {
+  takesClosure {
+  }
+}
diff --git a/test/Concurrency/attr_execution/nonisolated_nonsending_by_default.swift b/test/Concurrency/attr_execution/nonisolated_nonsending_by_default.swift
new file mode 100644
index 0000000000000..6c240ec88f364
--- /dev/null
+++ b/test/Concurrency/attr_execution/nonisolated_nonsending_by_default.swift
@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift -swift-version 6 -enable-upcoming-feature NonisolatedNonsendingByDefault %s
+
+// REQUIRES: swift_feature_NonisolatedNonsendingByDefault
+
+func testCasts() {
+  let defaultedType = (() async -> ()).self
+  _ = defaultedType as (@concurrent () async -> ()).Type
+  // expected-error@-1 {{cannot convert value of type '(nonisolated(nonsending) () async -> ()).Type' to type '(() async -> ()).Type' in coercion}}
+  _ = defaultedType as (nonisolated(nonsending) () async -> ()).Type // Ok
+}
diff --git a/test/SILGen/objc_async_from_swift.swift b/test/SILGen/objc_async_from_swift.swift
index 63e6f97efa4e7..5179077f1d35b 100644
--- a/test/SILGen/objc_async_from_swift.swift
+++ b/test/SILGen/objc_async_from_swift.swift
@@ -378,7 +378,8 @@ func testAutoclosureInStaticMethod() {
   final class TestKlass {
     // Default argument for method.
     //
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error) {
     //
     // Get standard.
     // CHECK: [[METATYPE:%.*]] = metatype $@objc_metatype SlowServer.Type
@@ -386,31 +387,37 @@ func testAutoclosureInStaticMethod() {
     // CHECK: [[STANDARD:%.*]] = apply [[GET_STANDARD_FUNC]]([[METATYPE]])
     //
     // Then grab value.
-    // CHECK: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error)
+    // CHECK-C: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error)
+    // CHECK-NN: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error)
     // CHECK: [[RESULT:%.*]] = apply [[GET_VALUE]]([[STANDARD]])
     //
     // Then we need to thunk to eliminate the implicit leading parameter. We use
     // the thunk that passes in .none so this acts as a concurrent function.
     //
-    // CHECK: [[THUNK_FN:%.*]] = function_ref @$sScA_pSgS2Ss5Error_pIegHgILgozo_S2SsAB_pIegHgozo_TR : $@convention(thin) @async (@guaranteed String, @guaranteed @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error)) -> (@owned String, @error any Error)
-    // CHECK: [[THUNKED:%.*]] = partial_apply [callee_guaranteed] [[THUNK_FN]]([[RESULT]])
-    // CHECK: return [[THUNKED]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_'
+    // CHECK-C: [[THUNK_FN:%.*]] = function_ref @$sScA_pSgS2Ss5Error_pIegHgILgozo_S2SsAB_pIegHgozo_TR : $@convention(thin) @async (@guaranteed String, @guaranteed @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error)) -> (@owned String, @error any Error)
+    // CHECK-C: [[THUNKED:%.*]] = partial_apply [callee_guaranteed] [[THUNK_FN]]([[RESULT]])
+    // CHECK-C: return [[THUNKED]]
+    // CHECK-NN: return [[RESULT]]
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_'
 
     // This is the first implicit closure. We close over self here.
     //
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error) {
     // CHECK: bb0([[SELF:%.*]] :
     //
     // Close over self and return it.
-    // CHECK:   [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
+    // CHECK-C:   [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
+    // CHECK-NN:  [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
     // CHECK:   [[SELF_COPY:%.*]] = copy_value [[SELF]]
     // CHECK:   [[CLOSE_OVER_SELF:%.*]] = partial_apply [callee_guaranteed] [[SECOND_CLOSURE]]([[SELF_COPY]])
     // CHECK:   return [[CLOSE_OVER_SELF]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_'
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_' 
 
     // The second closure. In this function we actually perform the objective-c call.
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_ : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
     // CHECK: bb0([[ACTOR:%.*]] : @guaranteed $Optional<any Actor>, [[ARG:%.*]] : @guaranteed $String, [[CAPTURE:%.*]] : @closureCapture @guaranteed $SlowServer):
     //
     // Hop to the actor
@@ -450,7 +457,8 @@ func testAutoclosureInStaticMethod() {
     // CHECK: [[ERROR_BB]]([[ERROR:%.*]] :
     // CHECK:   hop_to_executor [[ACTOR]]
     // CHECK:   throw [[ERROR]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_'
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKYCcSo10SlowServerCcfu_S2SYaKYCcfu0_'
 
     // Actual static method
     //
@@ -467,12 +475,12 @@ func testAutoclosureInStaticMethod() {
     // CHECK-C:   hop_to_executor [[EXEC_NONE]]
     // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ'
     //
-    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed @noescape @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error), @thick TestKlass.Type) -> @owned Optional<String> {
-    // CHECK-NN: bb0([[ACTOR:%.*]] : @guaranteed $Optional<any Actor>, [[STRING:%.*]] : @guaranteed $String, [[COMPLETION:%.*]] : @guaranteed $@noescape @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error), [[METATYPE:%.*]] : $@thick TestKlass.Type)
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZ : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed @noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error), @thick TestKlass.Type) -> @owned Optional<String> {
+    // CHECK-NN: bb0([[ACTOR:%.*]] : @guaranteed $Optional<any Actor>, [[STRING:%.*]] : @guaranteed $String, [[COMPLETION:%.*]] : @guaranteed $@noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error), %3 : $@thick TestKlass.Type):
     // CHECK-NN:   hop_to_executor [[ACTOR]]
     // CHECK-NN:   hop_to_executor [[ACTOR]]
     // CHECK-NN:   hop_to_executor [[ACTOR]]
-    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C8getValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZ'
     static func getValue(id: String,
                          valueForKey: (_ identifier: String) async throws -> String = SlowServer.standard.value(withKey:)) async -> String? {
       let result: String
@@ -486,7 +494,8 @@ func testAutoclosureInStaticMethod() {
 
     // Default argument for method.
     //
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_ : $@convention(thin) () -> @owned @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error) {
     //
     // Get standard.
     // CHECK: [[METATYPE:%.*]] = metatype $@objc_metatype SlowServer.Type
@@ -494,29 +503,38 @@ func testAutoclosureInStaticMethod() {
     // CHECK: [[STANDARD:%.*]] = apply [[GET_STANDARD_FUNC]]([[METATYPE]])
     //
     // Then grab value.
-    // CHECK: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error)
+    // CHECK-C: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error)
+    // CHECK-NN: [[GET_VALUE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error)
     // CHECK: [[RESULT:%.*]] = apply [[GET_VALUE]]([[STANDARD]])
     //
-    // CHECK: return [[RESULT]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_'
+    // CHECK-NN: [[THUNK:%.*]] = function_ref @$sS2Ss5Error_pIegHgozo_ScA_pSgS2SsAA_pIegHgILgozo_TR : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error)) -> (@owned String, @error any Error)
+    // CHECK-NN: [[THUNKED_RESULT:%.*]] = partial_apply [callee_guaranteed] [[THUNK]]([[RESULT]])
+    // CHECK-C: return [[RESULT]]
+    // CHECK-NN: return [[THUNKED_RESULT]]
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_'
 
     // This is the first implicit closure. We close over self here.
     //
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_ : $@convention(thin) (@guaranteed SlowServer) -> @owned @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error) {
     // CHECK: bb0([[SELF:%.*]] :
     //
     // Close over self and return it.
-    // CHECK:   [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
+    // CHECK-C:  [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
+    // CHECK-NN: [[SECOND_CLOSURE:%.*]] = function_ref @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error)
     // CHECK:   [[SELF_COPY:%.*]] = copy_value [[SELF]]
     // CHECK:   [[CLOSE_OVER_SELF:%.*]] = partial_apply [callee_guaranteed] [[SECOND_CLOSURE]]([[SELF_COPY]])
     // CHECK:   return [[CLOSE_OVER_SELF]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_'
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_'
 
     // The second closure. In this function we actually perform the objective-c call.
     //
     // It is main actor isolated.
     //
-    // CHECK-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
+    // CHECK-C-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_ : $@convention(thin) @async (@guaranteed String, @guaranteed SlowServer) -> (@owned String, @error any Error) {
     // CHECK: bb0([[ARG:%.*]] : @guaranteed $String, [[CAPTURE:%.*]] : @closureCapture @guaranteed $SlowServer):
     //
     // CHECK:   [[ACTOR:%.*]] = apply {{%.*}}({{%.*}}) : $@convention(method) (@thick MainActor.Type) -> @owned MainActor
@@ -558,7 +576,8 @@ func testAutoclosureInStaticMethod() {
     // CHECK: [[ERROR_BB]]([[ERROR:%.*]] :
     // CHECK:   hop_to_executor [[ACTOR_B]]
     // CHECK:   throw [[ERROR]]
-    // CHECK: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_'
+    // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZfA0_S2SYaKScMYccSo10SlowServerCcfu_S2SYaKScMYccfu0_'
 
     // Actual static method
     //
@@ -572,12 +591,12 @@ func testAutoclosureInStaticMethod() {
     // CHECK-C:   hop_to_executor [[EXEC_NONE]]
     // CHECK-C: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ'
     //
-    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed @noescape @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error), @thick TestKlass.Type) -> @owned Optional<String> {
-    // CHECK-NN: bb0([[ACTOR:%.*]] : @guaranteed $Optional<any Actor>, [[STRING:%.*]] : @guaranteed $String, [[COMPLETION:%.*]] : @guaranteed $@noescape @async @callee_guaranteed (@guaranteed String) -> (@owned String, @error any Error), [[METATYPE:%.*]] : $@thick TestKlass.Type)
+    // CHECK-NN-LABEL: sil private [ossa] @$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZ : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String, @guaranteed @noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error), @thick TestKlass.Type) -> @owned Optional<String> {
+    // CHECK-NN: bb0([[ACTOR:%.*]] : @guaranteed $Optional<any Actor>, [[STRING:%.*]] : @guaranteed $String, [[COMPLETION:%.*]] : @guaranteed $@noescape @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @guaranteed String) -> (@owned String, @error any Error), %3 : $@thick TestKlass.Type)
     // CHECK-NN:   hop_to_executor [[ACTOR]]
     // CHECK-NN:   hop_to_executor [[ACTOR]]
     // CHECK-NN:   hop_to_executor [[ACTOR]]
-    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKXEtYaFZ'
+    // CHECK-NN: } // end sil function '$s21objc_async_from_swift29testAutoclosureInStaticMethodyyF9TestKlassL_C17getMainActorValue2id11valueForKeySSSgSS_S2SYaKYCXEtYaFZ'
     static func getMainActorValue(id: String,
                                   valueForKey: (_ identifier: String) async throws -> String = SlowServer.standard.mainActorValue(withKey:)) async -> String? {
       let result: String