diff --git a/insns.dat b/insns.dat
index d9e669aa..28736524 100644
--- a/insns.dat
+++ b/insns.dat
@@ -766,6 +766,7 @@ LTR		reg16				\2\x0F\x00\203					286,PROT,PRIV
 MFENCE		void				\3\x0F\xAE\xF0					X64,AMD
 MONITOR		void				\3\x0F\x01\xC8					PRESCOTT
 MONITOR		reg_eax,reg_ecx,reg_edx		\3\x0F\x01\xC8					PRESCOTT,ND
+MONITOR		reg_rax,reg_ecx,reg_edx		\3\x0F\x01\xC8					X64,ND
 MOV		mem,reg_sreg			\1\x8C\101					8086,SM
 MOV		reg16,reg_sreg			\320\1\x8C\101					8086
 MOV		reg32,reg_sreg			\321\1\x8C\101					386