diff --git a/Makefile.am b/Makefile.am
index 051d34ba..e248ae54 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -414,7 +414,7 @@ dummy-vkd3d-version:
 ## Cross-compile tests
 cross_implibs = crosslibs/d3d12
 CROSS_CPPFLAGS = -I$(srcdir)/include -I$(srcdir)/include/private -I$(builddir)/include
-CROSS_CFLAGS = -g -O2 -Wall -municode ${CROSS_CPPFLAGS} -D__USE_MINGW_ANSI_STDIO=0
+CROSS_CFLAGS = -g -O2 -Wall -municode ${CROSS_CPPFLAGS} -D__USE_MINGW_ANSI_STDIO=0 -DVKD3D_CROSSTEST=1
 EXTRA_DIST += $(cross_implibs:=.cross32.def) $(cross_implibs:=.cross64.def)
 EXTRA_DIST += tests/shader_runner_d3d11.c tests/shader_runner_d3d9.c
 
diff --git a/tests/d3d12_crosstest.h b/tests/d3d12_crosstest.h
index e6dc7a6c..26f70018 100644
--- a/tests/d3d12_crosstest.h
+++ b/tests/d3d12_crosstest.h
@@ -56,7 +56,7 @@ typedef int HRESULT;
 #include <stddef.h>
 #include <time.h>
 
-#ifdef _WIN32
+#ifdef VKD3D_CROSSTEST
 # include "vkd3d_dxgi1_4.h"
 #else
 # define VKD3D_UTILS_API_VERSION VKD3D_API_VERSION_1_2
@@ -261,7 +261,7 @@ static void wait_queue_idle_(unsigned int line, ID3D12Device *device, ID3D12Comm
 static bool use_warp_device;
 static unsigned int use_adapter_idx;
 
-#ifdef _WIN32
+#ifdef VKD3D_CROSSTEST
 static IUnknown *create_warp_adapter(IDXGIFactory4 *factory)
 {
     IUnknown *adapter;
diff --git a/tests/shader_runner.c b/tests/shader_runner.c
index 0f205bfe..8e0ecc1a 100644
--- a/tests/shader_runner.c
+++ b/tests/shader_runner.c
@@ -1060,7 +1060,7 @@ out:
 
 START_TEST(shader_runner)
 {
-#ifdef _WIN32
+#ifdef VKD3D_CROSSTEST
     run_shader_tests_d3d9(argc, argv);
     run_shader_tests_d3d11(argc, argv);
 #else
diff --git a/tests/vkd3d_api.c b/tests/vkd3d_api.c
index ab266c4b..5a585fec 100644
--- a/tests/vkd3d_api.c
+++ b/tests/vkd3d_api.c
@@ -16,6 +16,23 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  */
 
+/* Hack for MinGW-w64 headers.
+ *
+ * We want to use WIDL C inline wrappers because some methods
+ * in D3D12 interfaces return aggregate objects. Unfortunately,
+ * WIDL C inline wrappers are broken when used with MinGW-w64
+ * headers because FORCEINLINE expands to extern inline
+ * which leads to the "multiple storage classes in declaration
+ * specifiers" compiler error.
+ */
+#ifdef __MINGW32__
+# include <_mingw.h>
+# ifdef __MINGW64_VERSION_MAJOR
+#  undef __forceinline
+#  define __forceinline __inline__ __attribute__((__always_inline__,__gnu_inline__))
+# endif
+#endif
+
 #define VK_NO_PROTOTYPES
 #define COBJMACROS
 #define INITGUID