diff --git a/src/expat/lib/internal.h b/src/expat/lib/internal.h
index 1bf6baa543..f7e9a98a5f 100644
--- a/src/expat/lib/internal.h
+++ b/src/expat/lib/internal.h
@@ -38,6 +38,9 @@
    Likely reason: __fastcall on Windows is like stdcall, therefore
    the compiler cannot perform stack optimizations for call clusters.
 */
+#ifdef FASTCALL
+#undef FASTCALL
+#endif
 #define FASTCALL
 #define PTRCALL
 #define PTRFASTCALL