diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 0f5b5b62c1e36..f5832366c242a 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -5954,8 +5954,7 @@ ERROR(concurrent_value_outside_source_file,none,
       "%kind0; use '@unchecked Sendable' for retroactive conformance",
       (const ValueDecl *))
 ERROR(concurrent_value_nonfinal_class,none,
-      "non-final class %0 cannot conform to 'Sendable'; "
-      "use '@unchecked Sendable'", (DeclName))
+      "non-final class %0 cannot conform to the 'Sendable' protocol", (DeclName))
 ERROR(concurrent_value_inherit,none,
       "'Sendable' class %1 cannot inherit from another class"
       "%select{| other than 'NSObject'}0",
diff --git a/lib/Sema/TypeCheckConcurrency.cpp b/lib/Sema/TypeCheckConcurrency.cpp
index 91a1bd921b1ad..c0932ff50ff2f 100644
--- a/lib/Sema/TypeCheckConcurrency.cpp
+++ b/lib/Sema/TypeCheckConcurrency.cpp
@@ -7265,9 +7265,9 @@ bool swift::checkSendableConformance(
 
     // An non-final class cannot conform to `Sendable`.
     if (!classDecl->isSemanticallyFinal()) {
-      classDecl->diagnose(diag::concurrent_value_nonfinal_class,
-                          classDecl->getName())
-        .limitBehaviorUntilSwiftVersion(behavior, 6);
+      classDecl->diagnose(diag::concurrent_value_nonfinal_class,classDecl->getName())
+          .fixItInsert(classDecl->getStartLoc(), "final")
+          .limitBehaviorUntilSwiftVersion(behavior, 6);
 
       if (behavior == DiagnosticBehavior::Unspecified)
         return true;
diff --git a/test/Concurrency/concurrency_warnings.swift b/test/Concurrency/concurrency_warnings.swift
index c9cc307fc77b4..d825ada3d9284 100644
--- a/test/Concurrency/concurrency_warnings.swift
+++ b/test/Concurrency/concurrency_warnings.swift
@@ -17,7 +17,7 @@ let rs = GlobalCounter() // expected-warning {{let 'rs' is not concurrency-safe
 
 import GlobalVariables
 
-class MyError: Error { // expected-warning{{non-final class 'MyError' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+class MyError: Error { // expected-warning{{non-final class 'MyError' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
   var storage = 0 // expected-warning{{stored property 'storage' of 'Sendable'-conforming class 'MyError' is mutable}}
 }
 
diff --git a/test/Concurrency/concurrent_value_checking.swift b/test/Concurrency/concurrent_value_checking.swift
index 0e0ec6dc66d9b..8f82db8dea898 100644
--- a/test/Concurrency/concurrent_value_checking.swift
+++ b/test/Concurrency/concurrent_value_checking.swift
@@ -375,7 +375,7 @@ extension C6_Restated_Extension: @unchecked Sendable {}
 
 final class C7<T>: Sendable { }
 
-class C9: Sendable { } // expected-warning{{non-final class 'C9' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+class C9: Sendable { } // expected-warning{{non-final class 'C9' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
 
 @available(*, unavailable)
 extension HasUnavailableSendable : @unchecked Sendable { }
diff --git a/test/Concurrency/sendable_conformance_checking.swift b/test/Concurrency/sendable_conformance_checking.swift
index 92475038fe3c7..5f77d9c7b7602 100644
--- a/test/Concurrency/sendable_conformance_checking.swift
+++ b/test/Concurrency/sendable_conformance_checking.swift
@@ -158,7 +158,7 @@ actor A10: AsyncThrowingProtocolWithNotSendable {
 }
 
 // rdar://86653457 - Crash due to missing Sendable conformances.
-// expected-warning @+1 {{non-final class 'Klass' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+// expected-warning @+1 {{non-final class 'Klass' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
 class Klass<Output: Sendable>: Sendable {}
 // expected-complete-and-tns-warning @+1 {{type 'S' does not conform to the 'Sendable' protocol}}
 final class SubKlass: Klass<[S]> {}
@@ -184,7 +184,7 @@ extension MultiConformance: @unchecked Sendable {} // expected-warning {{redunda
 
 @available(SwiftStdlib 5.1, *)
 actor MyActor {
-  // expected-warning@+1 {{non-final class 'Nested' cannot conform to 'Sendable'; use '@unchecked Sendable'; this is an error in the Swift 6 language mode}}
+  // expected-warning@+1 {{non-final class 'Nested' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
   class Nested: Sendable {}
 }
 
diff --git a/test/Concurrency/sendable_objc_protocol_attr.swift b/test/Concurrency/sendable_objc_protocol_attr.swift
index 15527a7a91a55..2b94fc80fa1eb 100644
--- a/test/Concurrency/sendable_objc_protocol_attr.swift
+++ b/test/Concurrency/sendable_objc_protocol_attr.swift
@@ -41,7 +41,7 @@ extension MyObjCProtocol {
 }
 
 class K : NSObject, MyObjCProtocol {
-  // expected-warning@-1 {{non-final class 'K' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-1 {{non-final class 'K' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
   let test: String = "k"
 }
 
@@ -50,7 +50,7 @@ class UncheckedK : NSObject, MyObjCProtocol, @unchecked Sendable { // ok
 }
 
 class KRefined : NSObject, MyRefinedObjCProtocol {
-  // expected-warning@-1 {{non-final class 'KRefined' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-1 {{non-final class 'KRefined' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
   let test: String = "refined"
 }
 
@@ -76,7 +76,7 @@ do {
   }
 
   class C : A, MyObjCProtocol {
-    // expected-warning@-1 {{non-final class 'C' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+    // expected-warning@-1 {{non-final class 'C' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
     // expected-warning@-2 {{'Sendable' class 'C' cannot inherit from another class other than 'NSObject'}}
     let test: String = "c"
   }
diff --git a/test/Distributed/actor_protocols.swift b/test/Distributed/actor_protocols.swift
index d3e728ff5de16..17717892517e4 100644
--- a/test/Distributed/actor_protocols.swift
+++ b/test/Distributed/actor_protocols.swift
@@ -95,7 +95,7 @@ actor A3: AnyActor {} // expected-warning {{'AnyActor' is deprecated: Use 'any A
 distributed actor DA3: AnyActor {} // expected-warning {{'AnyActor' is deprecated: Use 'any Actor' with 'DistributedActor.asLocalActor' instead}}
 
 class C3: AnyActor { // expected-warning {{'AnyActor' is deprecated: Use 'any Actor' with 'DistributedActor.asLocalActor' instead}}
-  // expected-warning@-1 {{non-final class 'C3' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-1 {{non-final class 'C3' cannot conform to the 'Sendable' protocol}}
 }
 
 struct S3: AnyActor { // expected-warning {{'AnyActor' is deprecated: Use 'any Actor' with 'DistributedActor.asLocalActor' instead}}
diff --git a/test/Macros/macro_expand_extensions.swift b/test/Macros/macro_expand_extensions.swift
index b333b7d12d802..7196eea12465a 100644
--- a/test/Macros/macro_expand_extensions.swift
+++ b/test/Macros/macro_expand_extensions.swift
@@ -269,7 +269,7 @@ macro AddSendable() = #externalMacro(module: "MacroDefinition", type: "SendableM
 final class SendableClass {
 }
 
-// expected-warning@+2 {{non-final class 'InvalidSendableClass' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+// expected-warning@+2 {{non-final class 'InvalidSendableClass' cannot conform to the 'Sendable' protocol}}
 @AddSendable
 class InvalidSendableClass {
 }
diff --git a/test/decl/class/actor/basic.swift b/test/decl/class/actor/basic.swift
index 72c784864848a..23749ee114d15 100644
--- a/test/decl/class/actor/basic.swift
+++ b/test/decl/class/actor/basic.swift
@@ -7,7 +7,7 @@ actor MyActor { }
 class MyActorSubclass1: MyActor { }
 // expected-error@-1{{actor types do not support inheritance}}
 // expected-error@-2{{type 'MyActorSubclass1' cannot conform to the 'Actor' protocol}}
-// expected-warning@-3 {{non-final class 'MyActorSubclass1' cannot conform to 'Sendable'; use '@unchecked Sendable'; this is an error in the Swift 6 language mode}}
+// expected-warning@-3 {{non-final class 'MyActorSubclass1' cannot conform to the 'Sendable' protocol; this is an error in the Swift 6 language mode}}
 
 actor MyActorSubclass2: MyActor { } // expected-error{{actor types do not support inheritance}}
 
diff --git a/test/decl/protocol/special/Actor.swift b/test/decl/protocol/special/Actor.swift
index 6e11f8628413c..9a42697489511 100644
--- a/test/decl/protocol/special/Actor.swift
+++ b/test/decl/protocol/special/Actor.swift
@@ -44,7 +44,7 @@ actor A7 {
 @available(SwiftStdlib 5.1, *)
 class C1: Actor {
   // expected-error@-1{{non-actor type 'C1' cannot conform to the 'Actor' protocol}}
-  // expected-warning@-2{{non-final class 'C1' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-2{{non-final class 'C1' cannot conform to the 'Sendable' protocol}}
   nonisolated var unownedExecutor: UnownedSerialExecutor {
     fatalError("")
   }
@@ -53,7 +53,7 @@ class C1: Actor {
 @available(SwiftStdlib 5.1, *)
 class C2: Actor {
   // expected-error@-1{{non-actor type 'C2' cannot conform to the 'Actor' protocol}}
-// expected-warning@-2{{non-final class 'C2' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-2{{non-final class 'C2' cannot conform to the 'Sendable' protocol}}
   // FIXME: this should be an isolation violation
   var unownedExecutor: UnownedSerialExecutor {
     fatalError("")
@@ -65,7 +65,7 @@ class C3: Actor {
   // expected-error@-1{{type 'C3' does not conform to protocol 'Actor'}}
   // expected-note@-2{{add stubs for conformance}}
   // expected-error@-3{{non-actor type 'C3' cannot conform to the 'Actor' protocol}}
-  // expected-warning@-4{{non-final class 'C3' cannot conform to 'Sendable'; use '@unchecked Sendable'}}
+  // expected-warning@-4{{non-final class 'C3' cannot conform to the 'Sendable' protocol}}
   nonisolated func enqueue(_ job: UnownedJob) { }
 }