diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index 4e4981a..3572029 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc
@@ -25,7 +25,7 @@
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/debug/alias.h"
-#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/prefs/pref_registry_simple.h"
 #include "components/session_manager/session_manager_types.h"
@@ -124,9 +124,10 @@
 
   authentication_stage_ = AuthenticationStage::kDoAuthenticate;
 
-  int dummy_value;
-  bool is_pin =
-      authenticated_by_pin && base::StringToInt(password, &dummy_value);
+  // Checking if the password is only formed of numbers with base::StringToInt
+  // will easily fail due to numeric limits. ContainsOnlyChars is used instead.
+  const bool is_pin =
+      authenticated_by_pin && base::ContainsOnlyChars(password, "0123456789");
   client_->AuthenticateUserWithPasswordOrPin(
       account_id, password, is_pin,
       base::BindOnce(&LoginScreenController::OnAuthenticateComplete,
diff --git a/ash/login/login_screen_controller_unittest.cc b/ash/login/login_screen_controller_unittest.cc
index 3d1f2e5..e60beff 100644
--- a/ash/login/login_screen_controller_unittest.cc
+++ b/ash/login/login_screen_controller_unittest.cc
@@ -70,7 +70,8 @@
       Shell::Get()->session_controller()->GetLastActiveUserPrefService();
   EXPECT_TRUE(prefs->FindPreference(prefs::kQuickUnlockPinSalt));
 
-  std::string pin = "123456";
+  // Use a long PIN (N > 2^64) for the test to ensure that there is no overflow.
+  std::string pin = "12345678901234567890";
   EXPECT_CALL(*client, AuthenticateUserWithPasswordOrPin_(id, pin, true, _));
   base::RunLoop run_loop2;
   controller->AuthenticateUserWithPasswordOrPin(