diff --git a/src/xrt/include/xrt/xrt_openxr_includes.h b/src/xrt/include/xrt/xrt_openxr_includes.h
index cc1859335..cb304e8bf 100644
--- a/src/xrt/include/xrt/xrt_openxr_includes.h
+++ b/src/xrt/include/xrt/xrt_openxr_includes.h
@@ -29,6 +29,10 @@ typedef void *GLXDrawable;
 typedef void *GLXContext;
 #endif
 
+#ifdef XR_USE_PLATFORM_WIN32
+#include <Unknwn.h>
+#endif
+
 #if defined(XR_USE_PLATFORM_EGL) || defined(XR_USE_GRAPHICS_API_OPENGL_ES)
 typedef void *EGLDisplay;
 typedef void *EGLContext;