diff --git a/src/lj_arch.h b/src/lj_arch.h
index c728742f..5e866fe4 100644
--- a/src/lj_arch.h
+++ b/src/lj_arch.h
@@ -107,6 +107,7 @@
 #define LJ_TARGET_EHRETREG	0
 #define LJ_TARGET_MASKSHIFT	1
 #define LJ_TARGET_MASKROT	1
+#define LJ_ARCH_DUALNUM		1
 
 #elif LUAJIT_TARGET == LUAJIT_ARCH_X64
 
@@ -120,6 +121,7 @@
 #define LJ_TARGET_EHRETREG	0
 #define LJ_TARGET_MASKSHIFT	1
 #define LJ_TARGET_MASKROT	1
+#define LJ_ARCH_DUALNUM		1
 
 #elif LUAJIT_TARGET == LUAJIT_ARCH_ARM
 
@@ -134,6 +136,7 @@
 #define LJ_TARGET_EHRETREG	0
 #define LJ_TARGET_MASKSHIFT	0
 #define LJ_TARGET_MASKROT	1
+#define LJ_ARCH_DUALNUM		2
 #define LJ_ARCH_NOFFI		1
 #define LJ_ARCH_NOJIT		1
 
@@ -154,6 +157,7 @@
 #define LJ_TARGET_EHRETREG	3
 #define LJ_TARGET_MASKSHIFT	0
 #define LJ_TARGET_MASKROT	1
+#define LJ_ARCH_DUALNUM		0
 #define LJ_ARCH_NOFFI		1	/* NYI: comparisons, calls. */
 #define LJ_ARCH_NOJIT		1
 
@@ -207,6 +211,14 @@
 #endif
 #endif
 
+/* Enable or disable the dual-number VM. */
+#if LJ_ARCH_DUALNUM == 2 || \
+    (defined(LUAJIT_ENABLE_DUALNUM) && LJ_ARCH_DUALNUM == 1)
+#define LJ_DUALNUM		1
+#else
+#define LJ_DUALNUM		0
+#endif
+
 /* Disable or enable the JIT compiler. */
 #if defined(LUAJIT_DISABLE_JIT) || defined(LJ_ARCH_NOJIT)
 #define LJ_HASJIT		0