diff --git a/components/password_manager/core/browser/password_autofill_manager_unittest.cc b/components/password_manager/core/browser/password_autofill_manager_unittest.cc
index 270d1342ea604..2ce71e8784323 100644
--- a/components/password_manager/core/browser/password_autofill_manager_unittest.cc
+++ b/components/password_manager/core/browser/password_autofill_manager_unittest.cc
@@ -1208,6 +1208,87 @@ TEST_F(PasswordAutofillManagerTest, FillsSuggestionIfAuthSuccessful) {
       SuggestionPosition{.row = 1});
 }
 
+// A DeviceAuthenticator that simulates DeviceAuthenticatorMac's
+// non-biometric path: AuthenticateWithMessage() synchronously runs a nested
+// event loop (modeled here as |on_nested_loop_|), during which the page that
+// owns the PasswordAutofillManager can be destroyed. After the nested loop
+// returns, the authenticator's own weak_this guard fires and the method
+// returns without touching members or running |callback| -- exactly what
+// device_authenticator_mac.mm does at lines 91-98 when weak_this is null.
+class NestedLoopDestroysOwnerAuthenticator
+    : public device_reauth::DeviceAuthenticator {
+ public:
+  explicit NestedLoopDestroysOwnerAuthenticator(base::OnceClosure on_nested_loop)
+      : on_nested_loop_(std::move(on_nested_loop)) {}
+  ~NestedLoopDestroysOwnerAuthenticator() override = default;
+
+  bool CanAuthenticateWithBiometrics() override { return false; }
+  bool CanAuthenticateWithBiometricOrScreenLock() override { return true; }
+  void Cancel() override {}
+  void AuthenticateWithMessage(const std::u16string& message,
+                               AuthenticateCallback callback) override {
+    // Snapshot the closure onto the stack: running it destroys |*this|
+    // (via ~PasswordAutofillManager -> CancelBiometricReauthIfOngoing ->
+    // authenticator_.reset()).
+    base::OnceClosure nested = std::move(on_nested_loop_);
+    // Drop |callback| like the production weak_this==null path does.
+    callback.Reset();
+    // Simulate the synchronous nested CFRunLoop that lets the opener
+    // destroy the popup's PasswordAutofillManager.
+    std::move(nested).Run();
+    // |*this| is now freed. Return without touching any members, just like
+    // device_authenticator_mac.mm:95-98 when weak_this is null.
+  }
+
+ private:
+  base::OnceClosure on_nested_loop_;
+};
+
+// Regression test: on macOS, AuthenticateWithMessage() can spin a nested
+// CFRunLoop (AuthorizationCopyRights) during which the RenderFrameHost owning
+// |this| PasswordAutofillManager is freed. The fix for the
+// DeviceAuthenticatorMac frame guards that frame, but DidAcceptSuggestion()
+// still dereferences member fields of |this| after the synchronous call
+// returns. Under ASAN this test produces a heap-use-after-free at the
+// password_client_->GetWebAuthnCredentialsDelegateForDriver() call.
+TEST_F(PasswordAutofillManagerTest,
+       DidAcceptSuggestion_ManagerFreedDuringSyncReauth_UAF) {
+  TestPasswordManagerClient client;
+  NiceMock<MockAutofillClient> autofill_client;
+  InitializePasswordAutofillManager(&client, &autofill_client);
+
+  password_autofill_manager_->ShowSuggestions(kTriggeringField);
+
+  // Force the reauth-before-filling path (production: macOS with the
+  // kBiometricAuthenticationBeforeFilling pref set and biometrics currently
+  // unavailable).
+  EXPECT_CALL(client, IsReauthBeforeFillingRequired).WillOnce(Return(true));
+  EXPECT_CALL(client, GetDeviceAuthenticator)
+      .WillOnce(Return(testing::ByMove(
+          std::make_unique<NestedLoopDestroysOwnerAuthenticator>(
+              base::BindOnce(
+                  [](std::unique_ptr<PasswordAutofillManager>* mgr) {
+                    // Simulates ContentPasswordManagerDriverFactory::
+                    // RenderFrameDeleted erasing the map node that owns the
+                    // by-value PasswordAutofillManager while the macOS
+                    // password dialog's nested run loop is spinning.
+                    mgr->reset();
+                  },
+                  &password_autofill_manager_)))));
+
+  // Hold a bare pointer the way AutofillPopupControllerImpl does after
+  // dereferencing its WeakPtr<AutofillSuggestionDelegate>.
+  PasswordAutofillManager* delegate = password_autofill_manager_.get();
+  delegate->DidAcceptSuggestion(
+      autofill::test::CreateAutofillSuggestion(
+          autofill::SuggestionType::kPasswordEntry, test_username_),
+      SuggestionPosition{.row = 1});
+  // If the bug is fixed, |delegate| was freed mid-call and DidAcceptSuggestion
+  // returned early without touching members. If not, ASAN reports a
+  // heap-use-after-free above.
+  EXPECT_EQ(password_autofill_manager_, nullptr);
+}
+
 TEST_F(PasswordAutofillManagerTest, DoesntFillSuggestionIfAuthFailed) {
   TestPasswordManagerClient client;
   NiceMock<MockAutofillClient> autofill_client;