diff --git a/app/code/Magento/Quote/Model/QuoteAddressValidator.php b/app/code/Magento/Quote/Model/QuoteAddressValidator.php
index 01d4632ec77c6..22f2f48850c48 100644
--- a/app/code/Magento/Quote/Model/QuoteAddressValidator.php
+++ b/app/code/Magento/Quote/Model/QuoteAddressValidator.php
@@ -122,7 +122,17 @@ public function validate(AddressInterface $addressData): bool
      */
     public function validateForCart(CartInterface $cart, AddressInterface $address): void
     {
-        $this->doValidate($address, $cart->getCustomerIsGuest() ? null : (int) $cart->getCustomer()->getId());
+        // If cart has a customer ID, use it regardless of the is_guest flag
+        // This handles cases where the flags are out of sync
+        $customerId = null;
+        if ($cart instanceof Quote) {
+            $customerId = $cart->getCustomerId();
+        } elseif (!$cart->getCustomerIsGuest()) {
+            $customer = $cart->getCustomer();
+            $customerId = $customer ? $customer->getId() : null;
+        }
+        
+        $this->doValidate($address, $customerId ? (int) $customerId : null);
     }
 
     /**
diff --git a/app/code/Magento/Quote/Test/Unit/Model/QuoteAddressValidatorTest.php b/app/code/Magento/Quote/Test/Unit/Model/QuoteAddressValidatorTest.php
new file mode 100644
index 0000000000000..10a400c34f51b
--- /dev/null
+++ b/app/code/Magento/Quote/Test/Unit/Model/QuoteAddressValidatorTest.php
@@ -0,0 +1,239 @@
+<?php
+/**
+ * Copyright 2024 Adobe
+ * All Rights Reserved.
+ */
+declare(strict_types=1);
+
+namespace Magento\Quote\Test\Unit\Model;
+
+use Magento\Customer\Api\AddressRepositoryInterface;
+use Magento\Customer\Api\CustomerRepositoryInterface;
+use Magento\Customer\Api\Data\AddressInterface as CustomerAddressInterface;
+use Magento\Customer\Api\Data\CustomerInterface;
+use Magento\Customer\Model\Session;
+use Magento\Framework\Exception\NoSuchEntityException;
+use Magento\Quote\Api\Data\AddressInterface;
+use Magento\Quote\Api\Data\CartInterface;
+use Magento\Quote\Model\Quote;
+use Magento\Quote\Model\QuoteAddressValidator;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+class QuoteAddressValidatorTest extends TestCase
+{
+    /**
+     * @var QuoteAddressValidator
+     */
+    private $validator;
+
+    /**
+     * @var AddressRepositoryInterface|MockObject
+     */
+    private $addressRepositoryMock;
+
+    /**
+     * @var CustomerRepositoryInterface|MockObject
+     */
+    private $customerRepositoryMock;
+
+    /**
+     * @var Session|MockObject
+     */
+    private $customerSessionMock;
+
+    /**
+     * @return void
+     */
+    protected function setUp(): void
+    {
+        $this->addressRepositoryMock = $this->getMockBuilder(AddressRepositoryInterface::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->customerRepositoryMock = $this->getMockBuilder(CustomerRepositoryInterface::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->customerSessionMock = $this->getMockBuilder(Session::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $this->validator = new QuoteAddressValidator(
+            $this->addressRepositoryMock,
+            $this->customerRepositoryMock,
+            $this->customerSessionMock
+        );
+    }
+
+    /**
+     * Test that validation uses customer ID when available, regardless of is_guest flag
+     *
+     * This tests the fix for the issue where is_guest flag and customer_id are out of sync
+     */
+    public function testValidateForCartWithCustomerIdIgnoresGuestFlag()
+    {
+        $customerId = 123;
+        $customerAddressId = 456;
+
+        $cartMock = $this->getMockBuilder(Quote::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customerMock = $this->getMockBuilder(CustomerInterface::class)
+            ->getMock();
+
+        $addressMock = $this->getMockBuilder(AddressInterface::class)
+            ->getMock();
+
+        $customerAddressMock = $this->getMockBuilder(CustomerAddressInterface::class)
+            ->getMock();
+
+        // Set up cart to have a customer ID
+        $cartMock->expects($this->once())
+            ->method('getCustomerId')
+            ->willReturn($customerId);
+
+        // Set up address with customer address ID
+        $addressMock->expects($this->once())
+            ->method('getCustomerAddressId')
+            ->willReturn($customerAddressId);
+
+        // Mock customer repository to return customer with addresses
+        $customerMock->expects($this->once())
+            ->method('getAddresses')
+            ->willReturn([$customerAddressMock]);
+
+        $customerAddressMock->expects($this->once())
+            ->method('getId')
+            ->willReturn($customerAddressId);
+
+        $this->customerRepositoryMock->expects($this->once())
+            ->method('getById')
+            ->with($customerId)
+            ->willReturn($customerMock);
+
+        $this->addressRepositoryMock->expects($this->once())
+            ->method('getById')
+            ->with($customerAddressId)
+            ->willReturn($customerAddressMock);
+
+        // Execute validation - should not throw exception
+        $this->validator->validateForCart($cartMock, $addressMock);
+    }
+
+    /**
+     * Test that validation correctly handles guest cart (no customer ID)
+     */
+    public function testValidateForCartWithGuestCart()
+    {
+        $cartMock = $this->getMockBuilder(Quote::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $addressMock = $this->getMockBuilder(AddressInterface::class)
+            ->getMock();
+
+        // Set up cart without customer ID (guest)
+        $cartMock->expects($this->once())
+            ->method('getCustomerId')
+            ->willReturn(null);
+
+        // Address should not have customer address ID for guest
+        $addressMock->expects($this->once())
+            ->method('getCustomerAddressId')
+            ->willReturn(null);
+
+        // Execute validation - should not throw exception
+        $this->validator->validateForCart($cartMock, $addressMock);
+    }
+
+    /**
+     * Test that validation throws exception when guest cart has customer address ID
+     */
+    public function testValidateForCartThrowsExceptionWhenGuestHasCustomerAddress()
+    {
+        $this->expectException(NoSuchEntityException::class);
+        $this->expectExceptionMessage('Invalid customer address id 456');
+
+        $customerAddressId = 456;
+
+        $cartMock = $this->getMockBuilder(Quote::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $addressMock = $this->getMockBuilder(AddressInterface::class)
+            ->getMock();
+
+        // Set up cart without customer ID (guest)
+        $cartMock->expects($this->once())
+            ->method('getCustomerId')
+            ->willReturn(null);
+
+        // Address has customer address ID even though cart is guest
+        $addressMock->expects($this->once())
+            ->method('getCustomerAddressId')
+            ->willReturn($customerAddressId);
+
+        // Execute validation - should throw exception
+        $this->validator->validateForCart($cartMock, $addressMock);
+    }
+
+    /**
+     * Test that validation throws exception when customer address doesn't belong to customer
+     */
+    public function testValidateForCartThrowsExceptionWhenAddressDoesNotBelongToCustomer()
+    {
+        $this->expectException(NoSuchEntityException::class);
+        $this->expectExceptionMessage('Invalid customer address id 456');
+
+        $customerId = 123;
+        $customerAddressId = 456;
+        $differentAddressId = 789;
+
+        $cartMock = $this->getMockBuilder(Quote::class)
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $customerMock = $this->getMockBuilder(CustomerInterface::class)
+            ->getMock();
+
+        $addressMock = $this->getMockBuilder(AddressInterface::class)
+            ->getMock();
+
+        $customerAddressMock = $this->getMockBuilder(CustomerAddressInterface::class)
+            ->getMock();
+
+        // Set up cart with customer ID
+        $cartMock->expects($this->once())
+            ->method('getCustomerId')
+            ->willReturn($customerId);
+
+        // Address has customer address ID
+        $addressMock->expects($this->once())
+            ->method('getCustomerAddressId')
+            ->willReturn($customerAddressId);
+
+        // Mock customer with different address
+        $customerMock->expects($this->once())
+            ->method('getAddresses')
+            ->willReturn([$customerAddressMock]);
+
+        $customerAddressMock->expects($this->once())
+            ->method('getId')
+            ->willReturn($differentAddressId);
+
+        $this->customerRepositoryMock->expects($this->once())
+            ->method('getById')
+            ->with($customerId)
+            ->willReturn($customerMock);
+
+        $this->addressRepositoryMock->expects($this->once())
+            ->method('getById')
+            ->with($customerAddressId)
+            ->willReturn($customerAddressMock);
+
+        // Execute validation - should throw exception
+        $this->validator->validateForCart($cartMock, $addressMock);
+    }
+}