diff -Nru mingw-w64-6.0.0/debian/changelog mingw-w64-6.0.0/debian/changelog
--- mingw-w64-6.0.0/debian/changelog	2018-10-24 20:20:36.000000000 +0000
+++ mingw-w64-6.0.0/debian/changelog	2018-11-11 19:47:29.000000000 +0000
@@ -1,3 +1,9 @@
+mingw-w64 (6.0.0-3) unstable; urgency=medium
+
+  * Fix widl build on aarch64.
+
+ -- Stephen Kitt <skitt@debian.org>  Sun, 11 Nov 2018 20:47:29 +0100
+
 mingw-w64 (6.0.0-2) unstable; urgency=medium
 
   * Ensure the build directory is created before writing to it.
diff -Nru mingw-w64-6.0.0/debian/patches/series mingw-w64-6.0.0/debian/patches/series
--- mingw-w64-6.0.0/debian/patches/series	2018-09-20 08:48:47.000000000 +0000
+++ mingw-w64-6.0.0/debian/patches/series	2018-11-11 17:39:17.000000000 +0000
@@ -8,3 +8,4 @@
 comutil-checkerror.patch
 genlib-lm.patch
 widl-pathtools-bsd.patch
+widl-windef-aarch64.patch
diff -Nru mingw-w64-6.0.0/debian/patches/widl-windef-aarch64.patch mingw-w64-6.0.0/debian/patches/widl-windef-aarch64.patch
--- mingw-w64-6.0.0/debian/patches/widl-windef-aarch64.patch	1970-01-01 00:00:00.000000000 +0000
+++ mingw-w64-6.0.0/debian/patches/widl-windef-aarch64.patch	2018-11-11 17:49:55.000000000 +0000
@@ -0,0 +1,16 @@
+Description: Fix widl build on aarch64
+Author: Stephen Kitt <skitt@debian.org>
+
+aarch64 doesn't have __builtin_ms_va_list, at least not in Debian.
+
+--- a/mingw-w64-tools/widl/include/windef.h
++++ b/mingw-w64-tools/widl/include/windef.h
+@@ -101,7 +101,7 @@
+ #endif /* __cdecl */
+ 
+ #ifndef __ms_va_list
+-# if (defined(__x86_64__) || defined(__aarch64__)) && defined (__GNUC__)
++# if defined(__x86_64__) && defined (__GNUC__)
+ #  define __ms_va_list __builtin_ms_va_list
+ #  define __ms_va_start(list,arg) __builtin_ms_va_start(list,arg)
+ #  define __ms_va_end(list) __builtin_ms_va_end(list)