diff --git a/lib/Sema/TypeCheckConcurrency.cpp b/lib/Sema/TypeCheckConcurrency.cpp
index 9cfe3bac19fc5..a75be814e8466 100644
--- a/lib/Sema/TypeCheckConcurrency.cpp
+++ b/lib/Sema/TypeCheckConcurrency.cpp
@@ -6513,6 +6513,20 @@ static InferredActorIsolation computeActorIsolation(Evaluator &evaluator,
       }
     }
 
+    // When `NonisolatedNonsendingByDefault` feature is enabled and the value is
+    // asynchronous `nonisolated` always means `nonisolated(nonsending)`.
+    if (ctx.LangOpts.hasFeature(Feature::NonisolatedNonsendingByDefault) &&
+        inferred.isNonisolated() && value->isAsync()) {
+      // Either current module or async variant of an ObjC API.
+      if (value->getModuleContext() == ctx.MainModule ||
+          (value->hasClangNode() &&
+           !isa<ProtocolDecl>(value->getDeclContext()))) {
+        inferred =
+            ActorIsolation::forCallerIsolationInheriting().withPreconcurrency(
+                inferred.preconcurrency());
+      }
+    }
+
     // Add an implicit attribute to capture the actor isolation that was
     // inferred, so that (e.g.) it will be printed and serialized.
     switch (inferred) {
@@ -6724,13 +6738,6 @@ static InferredActorIsolation computeActorIsolation(Evaluator &evaluator,
       if (shouldSelfIsolationOverrideDefault(
               ctx, value->getDeclContext(), selfTypeIsolation.isolation)) {
         auto isolation = selfTypeIsolation.isolation;
-
-        if (ctx.LangOpts.hasFeature(Feature::NonisolatedNonsendingByDefault) &&
-            value->isAsync() && value->getModuleContext() == ctx.MainModule &&
-            isolation.isNonisolated()) {
-          isolation = ActorIsolation::forCallerIsolationInheriting();
-        }
-
         return {inferredIsolation(isolation, onlyGlobal),
                 selfTypeIsolation.source};
       }
diff --git a/test/Concurrency/attr_execution/nonisolated_cross_module_with_flag_enabled.swift b/test/Concurrency/attr_execution/nonisolated_cross_module_with_flag_enabled.swift
index c952f4c9455dd..23561e8427d7e 100644
--- a/test/Concurrency/attr_execution/nonisolated_cross_module_with_flag_enabled.swift
+++ b/test/Concurrency/attr_execution/nonisolated_cross_module_with_flag_enabled.swift
@@ -47,6 +47,36 @@ public struct InferenceTest {
   public func testAutoclosure(value2 fn: nonisolated(nonsending) @autoclosure () async -> Int) async { await fn() }
 }
 
+// CHECK: nonisolated extension A.InferenceTest {
+// CHECK:   nonisolated(nonsending) public func testInExtension() async
+// CHECK:   @concurrent public func testConcurrentInExtension() async
+// CHECK: }
+nonisolated public extension InferenceTest {
+  func testInExtension() async {}
+  @concurrent func testConcurrentInExtension() async {}
+}
+
+// CHECK: public protocol P {
+// CHECK:   nonisolated(nonsending) func testWitness() async
+// CHECK: }
+public protocol P {
+  func testWitness() async
+}
+
+// CHECK: public struct WitnessTest : nonisolated A.P {
+// CHECK:   nonisolated(nonsending) public func testWitness() async
+// CHECK: }
+public struct WitnessTest: nonisolated P {
+  public func testWitness() async {}
+}
+
+// CHECK: nonisolated public class NoinsolatedClassTest {
+// CHECK:   nonisolated(nonsending) public func test() async
+// CHECK: }
+nonisolated public class NoinsolatedClassTest {
+  public func test() async {}
+}
+
 //--- Client.swift
 import A
 
@@ -75,6 +105,8 @@ func testWithCallback(t: Test) async {
 // CHECK: function_ref @$s1A13InferenceTestV10infersAttryyYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Builtin.ImplicitActor, @in_guaranteed InferenceTest) -> ()
 // CHECK: function_ref @$s1A13InferenceTestV10testNested8callbackyyyyYaYbYCXEc_tF : $@convention(method) (@guaranteed @callee_guaranteed (@guaranteed @noescape @Sendable @async @callee_guaranteed (@sil_isolated @sil_implicit_leading_param @guaranteed Builtin.ImplicitActor) -> ()) -> (), @in_guaranteed InferenceTest) -> ()
 // CHECK: function_ref @$s1A13InferenceTestV10testNested4dictySDySSyyYaYCcSgG_tF : $@convention(method) (@guaranteed Dictionary<String, Optional<nonisolated(nonsending) () async -> ()>>, @in_guaranteed InferenceTest) -> ()
+// CHECK: function_ref @$s1A13InferenceTestV15testInExtensionyyYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Builtin.ImplicitActor, @in_guaranteed InferenceTest) -> ()
+// CHECK: function_ref @$s1A13InferenceTestV25testConcurrentInExtensionyyYaF : $@convention(method) @async (@in_guaranteed InferenceTest) -> ()
 // CHECK: } // end sil function '$s6Client13testInference1ty1A0C4TestV_tYaF'
 @MainActor
 func testInference(t: InferenceTest) async {
@@ -82,6 +114,9 @@ func testInference(t: InferenceTest) async {
 
     t.testNested { _ in }
     t.testNested(dict: [:])
+
+    await t.testInExtension()
+    await t.testConcurrentInExtension()
 }
 
 // CHECK-LABEL: sil hidden @$s6Client15testAutoclosure1ty1A13InferenceTestV_tYaF : $@convention(thin) @async (@in_guaranteed InferenceTest) -> ()
@@ -92,3 +127,17 @@ func testAutoclosure(t: InferenceTest) async {
     await t.testAutoclosure(value1: 42)
     await t.testAutoclosure(value2: 42)
 }
+
+// CHECK-LABEL: sil hidden @$s6Client26testWitnessWithNonisolated1ty1A0C4TestV_tYaF : $@convention(thin) @async (@in_guaranteed WitnessTest) -> ()
+// CHECK: function_ref @$s1A11WitnessTestV04testA0yyYaF : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Builtin.ImplicitActor, @in_guaranteed WitnessTest) -> ()
+// CHECK: } // end sil function '$s6Client26testWitnessWithNonisolated1ty1A0C4TestV_tYaF'
+func testWitnessWithNonisolated(t: WitnessTest) async {
+  await t.testWitness()
+}
+
+// CHECK-LABEL: sil hidden @$s6Client20testNonisolatedClass1ty1A011NoinsolatedD4TestC_tYaF : $@convention(thin) @async (@guaranteed NoinsolatedClassTest) -> ()
+// CHECK: class_method {{.*}}, #NoinsolatedClassTest.test : (NoinsolatedClassTest) -> () async -> (), $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Builtin.ImplicitActor, @guaranteed NoinsolatedClassTest) -> ()
+// CHECK: } // end sil function '$s6Client20testNonisolatedClass1ty1A011NoinsolatedD4TestC_tYaF'
+func testNonisolatedClass(t: NoinsolatedClassTest) async {
+  await t.test()
+}
diff --git a/test/Concurrency/attr_execution/nonisolated_nonsending_by_default_and_objc_nonisolated.swift b/test/Concurrency/attr_execution/nonisolated_nonsending_by_default_and_objc_nonisolated.swift
new file mode 100644
index 0000000000000..bc765c78732a5
--- /dev/null
+++ b/test/Concurrency/attr_execution/nonisolated_nonsending_by_default_and_objc_nonisolated.swift
@@ -0,0 +1,44 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-sil %t/src/main.swift \
+// RUN:   -import-objc-header %t/src/Test.h \
+// RUN:   -swift-version 5 \
+// RUN:   -strict-concurrency=complete \
+// RUN:   -enable-upcoming-feature NonisolatedNonsendingByDefault \
+// RUN:   -module-name main -I %t -verify
+
+// REQUIRES: objc_interop
+// REQUIRES: concurrency
+// REQUIRES: swift_feature_NonisolatedNonsendingByDefault
+
+//--- Test.h
+#define SWIFT_NONISOLATED __attribute__((__swift_attr__("nonisolated")))
+
+#pragma clang assume_nonnull begin
+
+@import Foundation;
+
+SWIFT_NONISOLATED
+@interface Doc : NSObject
+- (void)saveWithCompletionHandler:(void (^ __nullable)(BOOL success))completionHandler;
+@end
+
+SWIFT_NONISOLATED
+@interface Doc(Reset)
+- (void)resetWithCompletionHandler:(void (^ __nullable)(BOOL success))completionHandler;
+@end
+
+#pragma clang assume_nonnull end
+
+//--- main.swift
+
+final class Test {
+  let doc = Doc()
+  
+  func test() async {
+    _ = await doc.save() // Ok
+    _ = await doc.reset() // Ok
+  }
+}