diff --git a/third_party/dawn/src/dawn/tests/white_box/SharedTextureMemoryYCbCrAndroidTests.cpp b/third_party/dawn/src/dawn/tests/white_box/SharedTextureMemoryYCbCrAndroidTests.cpp
index 154d3b748b5..356317ddddb 100644
--- a/third_party/dawn/src/dawn/tests/white_box/SharedTextureMemoryYCbCrAndroidTests.cpp
+++ b/third_party/dawn/src/dawn/tests/white_box/SharedTextureMemoryYCbCrAndroidTests.cpp
@@ -393,6 +393,58 @@ TEST_P(SharedTextureMemoryYCbCrVulkanSamplersTests,
     ASSERT_DEVICE_ERROR(memory.BeginAccess(texture, &beginDesc));
 }
 
+// POC: Dawn does not enforce VUID-VkSamplerCreateInfo-addressModeU-01646.
+// Creating a sampler with a YCbCr conversion attached and addressModeU/V/W !=
+// CLAMP_TO_EDGE is undefined behaviour per the Vulkan spec. Dawn's frontend
+// validation (dawn/native/Sampler.cpp ValidateSamplerDescriptor) does not reject
+// this, and dawn/native/vulkan/SamplerVk.cpp::Initialize passes the address modes
+// through unchanged.
+//
+// Run with --enable-backend-validation=full to observe the VVL error:
+//   VUID-VkSamplerCreateInfo-addressModeU-01646
+//   "If sampler YCbCr conversion is enabled, addressModeU, addressModeV, and
+//    addressModeW must be VK_SAMPLER_ADDRESS_MODE_CLAMP_TO_EDGE"
+TEST_P(SharedTextureMemoryYCbCrVulkanSamplersTests, YCbCrSamplerWithRepeatViolatesVUID01646) {
+    // Allocate a real multi-planar AHardwareBuffer so the driver sees a genuine
+    // external YCbCr format (matches what Chrome's VideoImageReaderImageBacking
+    // produces for HW-decoded <video> on Android).
+    AHardwareBuffer_Desc ahbDesc = {
+        .width = 4,
+        .height = 4,
+        .layers = 1,
+        .format = AHARDWAREBUFFER_FORMAT_Y8Cb8Cr8_420,
+        .usage = AHARDWAREBUFFER_USAGE_GPU_SAMPLED_IMAGE,
+    };
+    AHardwareBuffer* ahb = nullptr;
+    ASSERT_EQ(AHardwareBuffer_allocate(&ahbDesc, &ahb), 0);
+
+    // Get the YCbCr descriptor for this AHB exactly as Chrome's GPU process does
+    // (gpu/command_buffer/service/shared_image/video_image_reader_image_backing.cc).
+    wgpu::AHardwareBufferProperties ahbProps;
+    ASSERT_EQ(device.GetAHardwareBufferProperties(ahb, &ahbProps), wgpu::Status::Success);
+    wgpu::YCbCrVkDescriptor yCbCrDesc = ahbProps.yCbCrInfo;
+    ASSERT_TRUE(yCbCrDesc.externalFormat != 0 || yCbCrDesc.vkFormat != 0);
+
+    // This is the descriptor Skia Graphite-Dawn produces when a compromised
+    // renderer ships a PaintShader::MakeImage(video_mailbox, kRepeat, kRepeat)
+    // over RasterCHROMIUM (third_party/skia/src/gpu/graphite/dawn/DawnSampler.cpp
+    // and KeyHelpers.cpp ImageShaderBlock::AddBlock).
+    wgpu::SamplerDescriptor samplerDesc = {};
+    samplerDesc.addressModeU = wgpu::AddressMode::Repeat;  // attacker-controlled
+    samplerDesc.addressModeV = wgpu::AddressMode::Repeat;
+    samplerDesc.addressModeW = wgpu::AddressMode::Repeat;
+    samplerDesc.nextInChain = &yCbCrDesc;
+
+    // BUG: this passes Dawn frontend validation and reaches vkCreateSampler with
+    // addressModeU/V/W = VK_SAMPLER_ADDRESS_MODE_REPEAT and
+    // pNext = VkSamplerYcbcrConversionInfo. With VVL enabled this fires
+    // VUID-01646; without VVL the driver enters spec-undefined behaviour.
+    wgpu::Sampler sampler = device.CreateSampler(&samplerDesc);
+    EXPECT_NE(sampler, nullptr);
+
+    AHardwareBuffer_release(ahb);
+}
+
 DAWN_INSTANTIATE_TEST(SharedTextureMemoryYCbCrVulkanSamplersTests, VulkanBackend());
 
 // Define a test parameter struct to check all combinations of Vulkan YCbCr sampler models. Use enum