diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 232144ebd4a9f..6e005e032dc69 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -5234,8 +5234,8 @@ ERROR(concurrent_access_local,none,
         "use of local %kind0 in concurrently-executing code",
         (const ValueDecl *))
 ERROR(actor_isolated_keypath_component,none,
-      "cannot form key path to%select{| distributed}0 actor-isolated %kind1",
-      (bool, const ValueDecl *))
+      "cannot form key path to %0 %kind1",
+      (ActorIsolation, const ValueDecl *))
 ERROR(effectful_keypath_component,none,
       "cannot form key path to %0 with 'throws' or 'async'",
       (DescriptiveDeclKind))
diff --git a/lib/Sema/TypeCheckConcurrency.cpp b/lib/Sema/TypeCheckConcurrency.cpp
index 6287e6ded386b..2fdddb2079805 100644
--- a/lib/Sema/TypeCheckConcurrency.cpp
+++ b/lib/Sema/TypeCheckConcurrency.cpp
@@ -3319,8 +3319,8 @@ namespace {
       for (const auto &component : keyPath->getComponents()) {
         // The decl referred to by the path component cannot be within an actor.
         if (component.hasDeclRef()) {
-          auto concDecl = component.getDeclRef();
-          auto decl = concDecl.getDecl();
+          auto declRef = component.getDeclRef();
+          auto decl = declRef.getDecl();
           auto isolation = getActorIsolationForReference(
               decl, getDeclContext());
           switch (isolation) {
@@ -3330,13 +3330,22 @@ namespace {
             break;
 
           case ActorIsolation::GlobalActor:
-          case ActorIsolation::GlobalActorUnsafe:
-            // Disable global actor checking for now.
-            if (isolation.isGlobalActor() &&
-                !ctx.LangOpts.isSwiftVersionAtLeast(6))
+          case ActorIsolation::GlobalActorUnsafe: {
+            // Perform the check only in `complete` mode or
+            // stricter.
+            if (ctx.LangOpts.StrictConcurrencyLevel <
+                StrictConcurrency::Complete)
+              break;
+
+            auto result = ActorReferenceResult::forReference(
+                declRef, component.getLoc(), getDeclContext(),
+                kindOfUsage(decl, keyPath));
+
+            if (result == ActorReferenceResult::SameConcurrencyDomain)
               break;
 
             LLVM_FALLTHROUGH;
+          }
 
           case ActorIsolation::ActorInstance:
             // If this entity is always accessible across actors, just check
@@ -3352,11 +3361,17 @@ namespace {
               break;
             }
 
-            ctx.Diags.diagnose(component.getLoc(),
-                               diag::actor_isolated_keypath_component,
-                               isolation.isDistributedActor(),
-                               decl);
-            diagnosed = true;
+            {
+              auto diagnostic = ctx.Diags.diagnose(
+                  component.getLoc(), diag::actor_isolated_keypath_component,
+                  isolation, decl);
+
+              if (isolation == ActorIsolation::ActorInstance)
+                diagnosed = true;
+              else
+                diagnostic.warnUntilSwiftVersion(6);
+            }
+
             break;
           }
         }
diff --git a/test/Concurrency/actor_keypath_isolation.swift b/test/Concurrency/actor_keypath_isolation.swift
index de8d70ab1d65b..840a807b2412c 100644
--- a/test/Concurrency/actor_keypath_isolation.swift
+++ b/test/Concurrency/actor_keypath_isolation.swift
@@ -58,7 +58,7 @@ func tryKeyPathsMisc(d : Door) {
 
 func tryKeyPathsFromAsync() async {
     _ = \Door.unsafeGlobActor_immutable
-    _ = \Door.unsafeGlobActor_mutable // okay for now
+    _ = \Door.unsafeGlobActor_mutable // expected-warning {{cannot form key path to main actor-isolated property 'unsafeGlobActor_mutable'; this is an error in Swift 6}}
 }
 
 func tryNonSendable() {
@@ -69,7 +69,7 @@ func tryNonSendable() {
 
 func tryKeypaths() {
     _ = \Door.unsafeGlobActor_immutable
-    _ = \Door.unsafeGlobActor_mutable // okay for now
+    _ = \Door.unsafeGlobActor_mutable // expected-warning {{cannot form key path to main actor-isolated property 'unsafeGlobActor_mutable'; this is an error in Swift 6}}
 
     _ = \Door.immutable
     _ = \Door.globActor_immutable
@@ -84,7 +84,13 @@ func tryKeypaths() {
     let _ : PartialKeyPath<Door> = \.mutable // expected-error{{cannot form key path to actor-isolated property 'mutable'}}
     let _ : AnyKeyPath = \Door.mutable  // expected-error{{cannot form key path to actor-isolated property 'mutable'}}
 
-    _ = \Door.globActor_mutable // okay for now
+    _ = \Door.globActor_mutable // expected-warning {{cannot form key path to main actor-isolated property 'globActor_mutable'; this is an error in Swift 6}}
     _ = \Door.[0] // expected-error{{cannot form key path to actor-isolated subscript 'subscript(_:)'}}
-    _ = \Door.["hello"] // okay for now
+    _ = \Door.["hello"] // expected-warning {{cannot form key path to main actor-isolated subscript 'subscript(_:)'; this is an error in Swift 6}}
+}
+
+@MainActor func testGlobalActorRefInSameContext() {
+  _ = \Door.unsafeGlobActor_mutable // Ok
+  _ = \Door.globActor_mutable // Ok
+  _ = \Door.["hello"] // Ok
 }
diff --git a/test/Concurrency/actor_keypath_isolation_swift6.swift b/test/Concurrency/actor_keypath_isolation_swift6.swift
index 0a314d411c441..60f7bacdae1ad 100644
--- a/test/Concurrency/actor_keypath_isolation_swift6.swift
+++ b/test/Concurrency/actor_keypath_isolation_swift6.swift
@@ -57,7 +57,7 @@ func tryKeyPathsMisc(d : Door) {
 
 func tryKeyPathsFromAsync() async {
     _ = \Door.unsafeGlobActor_immutable
-    _ = \Door.unsafeGlobActor_mutable // expected-error {{cannot form key path to actor-isolated property 'unsafeGlobActor_mutable'}}
+    _ = \Door.unsafeGlobActor_mutable // expected-error {{cannot form key path to main actor-isolated property 'unsafeGlobActor_mutable'}}
 }
 
 func tryNonSendable() {
@@ -68,7 +68,7 @@ func tryNonSendable() {
 
 func tryKeypaths() {
     _ = \Door.unsafeGlobActor_immutable
-    _ = \Door.unsafeGlobActor_mutable // expected-error {{cannot form key path to actor-isolated property 'unsafeGlobActor_mutable'}}
+    _ = \Door.unsafeGlobActor_mutable // expected-error {{cannot form key path to main actor-isolated property 'unsafeGlobActor_mutable'}}
 
     _ = \Door.immutable
     _ = \Door.globActor_immutable
@@ -83,7 +83,13 @@ func tryKeypaths() {
     let _ : PartialKeyPath<Door> = \.mutable // expected-error{{cannot form key path to actor-isolated property 'mutable'}}
     let _ : AnyKeyPath = \Door.mutable  // expected-error{{cannot form key path to actor-isolated property 'mutable'}}
 
-    _ = \Door.globActor_mutable // expected-error{{cannot form key path to actor-isolated property 'globActor_mutable'}}
+    _ = \Door.globActor_mutable // expected-error{{cannot form key path to main actor-isolated property 'globActor_mutable'}}
     _ = \Door.[0] // expected-error{{cannot form key path to actor-isolated subscript 'subscript(_:)'}}
-    _ = \Door.["hello"] // expected-error {{cannot form key path to actor-isolated subscript 'subscript(_:)'}}
+    _ = \Door.["hello"] // expected-error {{cannot form key path to main actor-isolated subscript 'subscript(_:)'}}
+}
+
+@MainActor func testGlobalActorRefInSameContext() {
+  _ = \Door.unsafeGlobActor_mutable // Ok
+  _ = \Door.globActor_mutable // Ok
+  _ = \Door.["hello"] // Ok
 }
diff --git a/test/Concurrency/global_actor_keypath_non_strict.swift b/test/Concurrency/global_actor_keypath_non_strict.swift
new file mode 100644
index 0000000000000..d9c5f86f6655c
--- /dev/null
+++ b/test/Concurrency/global_actor_keypath_non_strict.swift
@@ -0,0 +1,25 @@
+// RUN: %target-swift-frontend  -disable-availability-checking %s -emit-sil -o /dev/null -verify
+
+// REQUIRES: concurrency && asserts
+
+actor Door {
+    @MainActor var globActor_mutable : Int = 0
+    @MainActor(unsafe) var unsafeGlobActor_mutable : Int = 0
+    @MainActor subscript(byName: String) -> Int { 0 }
+}
+
+func tryKeyPathsFromAsync() async {
+    _ = \Door.unsafeGlobActor_mutable // no warning
+}
+
+func tryKeypaths() {
+    _ = \Door.unsafeGlobActor_mutable // no warning
+    _ = \Door.globActor_mutable // no warning
+    _ = \Door.["hello"] // no warning
+}
+
+@MainActor func testGlobalActorRefInSameContext() {
+  _ = \Door.unsafeGlobActor_mutable // Ok
+  _ = \Door.globActor_mutable // Ok
+  _ = \Door.["hello"] // Ok
+}