diff --git a/src/Makefile b/src/Makefile
index 991a02f0..58dcdc01 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -362,6 +362,9 @@ DASM_XFLAGS=
 DASM_AFLAGS=
 DASM_ARCH= $(TARGET_LJARCH)
 
+ifneq (,$(findstring LJ_ARCH_BITS 64,$(TARGET_TESTARCH)))
+  DASM_AFLAGS+= -D P64
+endif
 ifneq (,$(findstring LJ_HASJIT 1,$(TARGET_TESTARCH)))
   DASM_AFLAGS+= -D JIT
 endif
@@ -387,7 +390,6 @@ ifeq (x86,$(TARGET_LJARCH))
   endif
 else
 ifeq (x64,$(TARGET_LJARCH))
-  DASM_AFLAGS+= -D X64
   DASM_ARCH= x86
 else
 ifeq (arm,$(TARGET_LJARCH))
diff --git a/src/vm_x86.dasc b/src/vm_x86.dasc
index 3520510a..44199606 100644
--- a/src/vm_x86.dasc
+++ b/src/vm_x86.dasc
@@ -2,7 +2,7 @@
 |// Bytecode interpreter, fast functions and helper functions.
 |// Copyright (C) 2005-2012 Mike Pall. See Copyright Notice in luajit.h
 |
-|.if X64
+|.if P64
 |.arch x64
 |.else
 |.arch x86
@@ -16,7 +16,8 @@
 |
 |//-----------------------------------------------------------------------
 |
-|.if X64
+|.if P64
+|.define X64, 1
 |.define SSE, 1
 |.if WIN
 |.define X64WIN, 1