diff --git a/src/dawn_native/Surface.cpp b/src/dawn_native/Surface.cpp
index 3a68832c28..d78f3f3cf3 100644
--- a/src/dawn_native/Surface.cpp
+++ b/src/dawn_native/Surface.cpp
@@ -124,11 +124,9 @@ namespace dawn_native {
             mType = Type::MetalLayer;
             mMetalLayer = metalDesc->layer;
         } else if (hwndDesc) {
-#if defined(DAWN_PLATFORM_WIN32)
             mType = Type::WindowsHWND;
             mHInstance = hwndDesc->hinstance;
             mHWND = hwndDesc->hwnd;
-#endif  // defined(DAWN_PLATFORM_WIN32)
         } else if (coreWindowDesc) {
 #if defined(DAWN_PLATFORM_WINDOWS)
             mType = Type::WindowsCoreWindow;
@@ -180,7 +178,7 @@ namespace dawn_native {
         return mHWND;
     }
 
-    void* Surface::GetCoreWindow() const {
+    IUnknown* Surface::GetCoreWindow() const {
         ASSERT(mType == Type::WindowsCoreWindow);
 #if defined(DAWN_PLATFORM_WINDOWS)
         return mCoreWindow.Get();
diff --git a/src/dawn_native/Surface.h b/src/dawn_native/Surface.h
index 2871bbb1ab..bdab2b45bc 100644
--- a/src/dawn_native/Surface.h
+++ b/src/dawn_native/Surface.h
@@ -27,6 +27,11 @@
 #    include "dawn_native/d3d12/d3d12_platform.h"
 #endif  // defined(DAWN_PLATFORM_WINDOWS)
 
+// Forward declare IUnknown
+// GetCoreWindow needs to return an IUnknown pointer
+// non-windows platforms don't have this type
+struct IUnknown;
+
 namespace dawn_native {
 
     MaybeError ValidateSurfaceDescriptor(const InstanceBase* instance,
@@ -57,7 +62,7 @@ namespace dawn_native {
         void* GetHWND() const;
 
         // Valid to call if the type is WindowsCoreWindow
-        void* GetCoreWindow() const;
+        IUnknown* GetCoreWindow() const;
 
         // Valid to call if the type is WindowsXlib
         void* GetXDisplay() const;
diff --git a/src/dawn_native/d3d12/SwapChainD3D12.cpp b/src/dawn_native/d3d12/SwapChainD3D12.cpp
index 166551338c..9002cc4c2d 100644
--- a/src/dawn_native/d3d12/SwapChainD3D12.cpp
+++ b/src/dawn_native/d3d12/SwapChainD3D12.cpp
@@ -245,7 +245,6 @@ namespace dawn_native { namespace d3d12 {
 
         ComPtr<IDXGISwapChain1> swapChain1;
         switch (GetSurface()->GetType()) {
-#if defined(DAWN_PLATFORM_WIN32)
             case Surface::Type::WindowsHWND: {
                 DAWN_TRY(CheckHRESULT(
                     factory2->CreateSwapChainForHwnd(device->GetCommandQueue().Get(),
@@ -254,13 +253,12 @@ namespace dawn_native { namespace d3d12 {
                     "Creating the IDXGISwapChain1"));
                 break;
             }
-#endif  // defined(DAWN_PLATFORM_WIN32)
             case Surface::Type::WindowsCoreWindow: {
-                DAWN_TRY(CheckHRESULT(factory2->CreateSwapChainForCoreWindow(
-                                          device->GetCommandQueue().Get(),
-                                          static_cast<IUnknown*>(GetSurface()->GetCoreWindow()),
-                                          &swapChainDesc, nullptr, &swapChain1),
-                                      "Creating the IDXGISwapChain1"));
+                DAWN_TRY(CheckHRESULT(
+                    factory2->CreateSwapChainForCoreWindow(device->GetCommandQueue().Get(),
+                                                           GetSurface()->GetCoreWindow(),
+                                                           &swapChainDesc, nullptr, &swapChain1),
+                    "Creating the IDXGISwapChain1"));
                 break;
             }
             default: