diff --git a/Modules/_ctypes/libffi_msvc/ffitarget.h b/Modules/_ctypes/libffi_msvc/ffitarget.h
index 0da79d4c1ad..85f5ee81bbe 100644
--- a/Modules/_ctypes/libffi_msvc/ffitarget.h
+++ b/Modules/_ctypes/libffi_msvc/ffitarget.h
@@ -36,7 +36,11 @@
 /* ---- Generic type definitions ----------------------------------------- */
 
 #ifndef LIBFFI_ASM
+#ifndef _WIN64
 typedef unsigned long          ffi_arg;
+#else
+typedef unsigned __int64       ffi_arg;
+#endif
 typedef signed long            ffi_sarg;
 
 typedef enum ffi_abi {