diff --git a/gfx/thebes/AllOfDcomp.h b/gfx/thebes/AllOfDcomp.h
new file mode 100644
index 000000000000..5b43182a5c6d
--- /dev/null
+++ b/gfx/thebes/AllOfDcomp.h
@@ -0,0 +1,39 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_gfx_AllOfDcomp_h
+#define mozilla_gfx_AllOfDcomp_h
+
+// Getting everything that we need in dcomp.h defined means messing with some defines.
+
+#if (_WIN32_WINNT < _WIN32_WINNT_WIN10)
+
+#  define XSTR(x) STR(x)
+#  define STR(x) #x
+// clang-format off
+
+#  pragma message "IDCompositionFilterEffect in dcomp.h requires _WIN32_WINNT >= _WIN32_WINNT_WIN10."
+// Pedantically, it actually requires _WIN32_WINNT_WINTHRESHOLD, but that's the
+// same as _WIN32_WINNT_WIN10.
+
+#  pragma message "Forcing NTDDI_VERSION " XSTR(NTDDI_VERSION) " -> " XSTR(NTDDI_WIN10)
+#  undef NTDDI_VERSION
+#  define NTDDI_VERSION NTDDI_WIN10
+
+#  pragma message "Forcing _WIN32_WINNT " XSTR(_WIN32_WINNT) " -> " XSTR(_WIN32_WINNT_WIN10)
+#  undef _WIN32_WINNT
+#  define _WIN32_WINNT _WIN32_WINNT_WIN10
+
+// clang-format on
+#  undef STR
+#  undef XSTR
+
+#endif
+
+// -
+
+#include <dcomp.h>
+
+#endif  // mozilla_gfx_AllOfDcomp_h
diff --git a/gfx/thebes/DeviceManagerDx.cpp b/gfx/thebes/DeviceManagerDx.cpp
index e99d360b5ed0..100cd3192afc 100644
--- a/gfx/thebes/DeviceManagerDx.cpp
+++ b/gfx/thebes/DeviceManagerDx.cpp
@@ -25,17 +25,10 @@
 #include "nsPrintfCString.h"
 #include "nsString.h"
 
-#undef _WIN32_WINNT
-#define _WIN32_WINNT _WIN32_WINNT_WINBLUE
-#undef NTDDI_VERSION
-#define NTDDI_VERSION NTDDI_WINBLUE
-
-// We also need this, or dcomp.h won't give us e.g. IDCompositionDevice3:
-#undef _WIN32_WINNT_WINTHRESHOLD
-#define _WIN32_WINNT_WINTHRESHOLD _WIN32_WINNT
+// -
 
+#include "mozilla/gfx/AllOfDcomp.h"
 #include <d3d11.h>
-#include <dcomp.h>
 #include <ddraw.h>
 #include <dxgi.h>
 
diff --git a/gfx/thebes/moz.build b/gfx/thebes/moz.build
index 176cc3c7e5db..9a87ea6aa0b0 100644
--- a/gfx/thebes/moz.build
+++ b/gfx/thebes/moz.build
@@ -67,6 +67,7 @@ EXPORTS += [
 ]
 
 EXPORTS.mozilla.gfx += [
+    "AllOfDcomp.h",
     "D3D11Checks.h",
     "DeviceManagerDx.h",
     "DisplayConfigWindows.h",
diff --git a/gfx/webrender_bindings/DCLayerTree.cpp b/gfx/webrender_bindings/DCLayerTree.cpp
index 2e738d4855fe..2faba766f76c 100644
--- a/gfx/webrender_bindings/DCLayerTree.cpp
+++ b/gfx/webrender_bindings/DCLayerTree.cpp
@@ -8,33 +8,9 @@
 
 // -
 
-#if (_WIN32_WINNT < _WIN32_WINNT_WIN10)
-
-#  define XSTR(x) STR(x)
-#  define STR(x) #x
-// clang-format off
-
-#  pragma message "IDCompositionFilterEffect in dcomp.h requires _WIN32_WINNT >= _WIN32_WINNT_WIN10."
-// Pedantically, it actually requires _WIN32_WINNT_WINTHRESHOLD, but that's the
-// same as _WIN32_WINNT_WIN10.
-
-#  pragma message "Forcing NTDDI_VERSION " XSTR(NTDDI_VERSION) " -> " XSTR(NTDDI_WIN10)
-#  undef NTDDI_VERSION
-#  define NTDDI_VERSION NTDDI_WIN10
-
-#  pragma message "Forcing _WIN32_WINNT " XSTR(_WIN32_WINNT) " -> " XSTR(_WIN32_WINNT_WIN10)
-#  undef _WIN32_WINNT
-#  define _WIN32_WINNT _WIN32_WINNT_WIN10
-
-// clang-format on
-#  undef STR
-#  undef XSTR
-
-#endif
-
+#include "mozilla/gfx/AllOfDcomp.h"
 #include <d3d11.h>
 #include <d3d11_1.h>
-#include <dcomp.h>
 #include <dxgi1_2.h>
 
 // -
@@ -57,6 +33,16 @@
 #include "nsPrintfCString.h"
 #include "WinUtils.h"
 
+// -
+
+#if defined(__MINGW32__)  // 64 defines both 32 and 64
+// We need to fake some things, while we wait on updates to mingw's dcomp.h
+// header. Just enough that we can successfully fail to work there.
+#define MOZ_MINGW_DCOMP_H_INCOMPLETE
+struct IDCompositionColorMatrixEffect : public IDCompositionFilterEffect {};
+struct IDCompositionTableTransferEffect : public IDCompositionFilterEffect {};
+#endif  // defined(__MINGW32__)
+
 namespace mozilla {
 namespace wr {
 
@@ -1820,6 +1806,8 @@ ColorManagementChain ColorManagementChain::From(
     const color::ColorProfileConversionDesc& conv) {
   auto ret = ColorManagementChain{};
 
+#if !defined(MOZ_MINGW_DCOMP_H_INCOMPLETE)
+
   const auto Append = [&](const RefPtr<IDCompositionFilterEffect>& afterLast) {
     if (ret.last) {
       afterLast->SetInput(0, ret.last, 0);
@@ -1855,6 +1843,9 @@ ColorManagementChain ColorManagementChain::From(
   ret.dstLinearFromSrcLinear =
       MaybeAppendColorMatrix(color::mat4(conv.dstLinearFromSrcLinear));
   ret.dstTfFromDstLinear = MaybeAppendTableTransfer(conv.dstTfFromDstLinear);
+
+#endif  // !defined(MOZ_MINGW_DCOMP_H_INCOMPLETE)
+
   return ret;
 }