diff --git a/include/windef.h b/include/windef.h
index 689163accc8..436ac6afd87 100644
--- a/include/windef.h
+++ b/include/windef.h
@@ -102,7 +102,7 @@ extern "C" {
 # define __fastcall __stdcall
 #endif
 
-#ifndef __thiscall
+#if (!defined(_MSC_VER) || !defined(__clang__)) && !defined(__thiscall)
 # define __thiscall __stdcall
 #endif
 
diff --git a/include/wine/asm.h b/include/wine/asm.h
index 3f5a685bb6b..a0367446745 100644
--- a/include/wine/asm.h
+++ b/include/wine/asm.h
@@ -96,7 +96,7 @@
 
 /* thiscall support */
 
-#if defined(__i386__) && !defined(__MINGW32__)
+#if defined(__i386__) && !defined(__MINGW32__) && (!defined(_MSC_VER) || !defined(__clang__))
 
 # ifdef _MSC_VER
 #  define DEFINE_THISCALL_WRAPPER(func,args) \