diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h
index 2866fddd184..c2487d2aca2 100644
--- a/arch/x86/include/asm/inat.h
+++ b/arch/x86/include/asm/inat.h
@@ -30,10 +30,11 @@
 #define INAT_OPCODE_TABLE_SIZE 256
 #define INAT_GROUP_TABLE_SIZE 8
 
-/* Legacy instruction prefixes */
+/* Legacy last prefixes */
 #define INAT_PFX_OPNDSZ	1	/* 0x66 */ /* LPFX1 */
 #define INAT_PFX_REPNE	2	/* 0xF2 */ /* LPFX2 */
 #define INAT_PFX_REPE	3	/* 0xF3 */ /* LPFX3 */
+/* Other Legacy prefixes */
 #define INAT_PFX_LOCK	4	/* 0xF0 */
 #define INAT_PFX_CS	5	/* 0x2E */
 #define INAT_PFX_DS	6	/* 0x3E */
@@ -42,8 +43,11 @@
 #define INAT_PFX_GS	9	/* 0x65 */
 #define INAT_PFX_SS	10	/* 0x36 */
 #define INAT_PFX_ADDRSZ	11	/* 0x67 */
+/* x86-64 REX prefix */
+#define INAT_PFX_REX	12	/* 0x4X */
 
-#define INAT_LPREFIX_MAX	3
+#define INAT_LSTPFX_MAX	3
+#define INAT_LGCPFX_MAX	11
 
 /* Immediate size */
 #define INAT_IMM_BYTE		1
@@ -75,12 +79,11 @@
 #define INAT_IMM_MASK	(((1 << INAT_IMM_BITS) - 1) << INAT_IMM_OFFS)
 /* Flags */
 #define INAT_FLAG_OFFS	(INAT_IMM_OFFS + INAT_IMM_BITS)
-#define INAT_REXPFX	(1 << INAT_FLAG_OFFS)
-#define INAT_MODRM	(1 << (INAT_FLAG_OFFS + 1))
-#define INAT_FORCE64	(1 << (INAT_FLAG_OFFS + 2))
-#define INAT_SCNDIMM	(1 << (INAT_FLAG_OFFS + 3))
-#define INAT_MOFFSET	(1 << (INAT_FLAG_OFFS + 4))
-#define INAT_VARIANT	(1 << (INAT_FLAG_OFFS + 5))
+#define INAT_MODRM	(1 << (INAT_FLAG_OFFS))
+#define INAT_FORCE64	(1 << (INAT_FLAG_OFFS + 1))
+#define INAT_SCNDIMM	(1 << (INAT_FLAG_OFFS + 2))
+#define INAT_MOFFSET	(1 << (INAT_FLAG_OFFS + 3))
+#define INAT_VARIANT	(1 << (INAT_FLAG_OFFS + 4))
 /* Attribute making macros for attribute tables */
 #define INAT_MAKE_PREFIX(pfx)	(pfx << INAT_PFX_OFFS)
 #define INAT_MAKE_ESCAPE(esc)	(esc << INAT_ESC_OFFS)
@@ -97,9 +100,10 @@ extern insn_attr_t inat_get_group_attribute(insn_byte_t modrm,
 					    insn_attr_t esc_attr);
 
 /* Attribute checking functions */
-static inline int inat_is_prefix(insn_attr_t attr)
+static inline int inat_is_legacy_prefix(insn_attr_t attr)
 {
-	return attr & INAT_PFX_MASK;
+	attr &= INAT_PFX_MASK;
+	return attr && attr <= INAT_LGCPFX_MAX;
 }
 
 static inline int inat_is_address_size_prefix(insn_attr_t attr)
@@ -112,9 +116,14 @@ static inline int inat_is_operand_size_prefix(insn_attr_t attr)
 	return (attr & INAT_PFX_MASK) == INAT_PFX_OPNDSZ;
 }
 
+static inline int inat_is_rex_prefix(insn_attr_t attr)
+{
+	return (attr & INAT_PFX_MASK) == INAT_PFX_REX;
+}
+
 static inline int inat_last_prefix_id(insn_attr_t attr)
 {
-	if ((attr & INAT_PFX_MASK) > INAT_LPREFIX_MAX)
+	if ((attr & INAT_PFX_MASK) > INAT_LSTPFX_MAX)
 		return 0;
 	else
 		return attr & INAT_PFX_MASK;
@@ -155,11 +164,6 @@ static inline int inat_immediate_size(insn_attr_t attr)
 	return (attr & INAT_IMM_MASK) >> INAT_IMM_OFFS;
 }
 
-static inline int inat_is_rex_prefix(insn_attr_t attr)
-{
-	return attr & INAT_REXPFX;
-}
-
 static inline int inat_has_modrm(insn_attr_t attr)
 {
 	return attr & INAT_MODRM;
diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index dfd56a30053..9f483179a8a 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -69,7 +69,7 @@ void insn_get_prefixes(struct insn *insn)
 	lb = 0;
 	b = peek_next(insn_byte_t, insn);
 	attr = inat_get_opcode_attribute(b);
-	while (inat_is_prefix(attr)) {
+	while (inat_is_legacy_prefix(attr)) {
 		/* Skip if same prefix */
 		for (i = 0; i < nb; i++)
 			if (prefixes->bytes[i] == b)
diff --git a/arch/x86/tools/gen-insn-attr-x86.awk b/arch/x86/tools/gen-insn-attr-x86.awk
index 19ba096b7dd..7d5492951e2 100644
--- a/arch/x86/tools/gen-insn-attr-x86.awk
+++ b/arch/x86/tools/gen-insn-attr-x86.awk
@@ -278,7 +278,7 @@ function convert_operands(opnd,       i,imm,mod)
 
 		# check REX prefix
 		if (match(opcode, rex_expr))
-			flags = add_flags(flags, "INAT_REXPFX")
+			flags = add_flags(flags, "INAT_MAKE_PREFIX(INAT_PFX_REX)")
 
 		# check coprocessor escape : TODO
 		if (match(opcode, fpu_expr))
@@ -316,7 +316,7 @@ END {
 	# print escape opcode map's array
 	print "/* Escape opcode map array */"
 	print "const insn_attr_t const *inat_escape_tables[INAT_ESC_MAX + 1]" \
-	      "[INAT_LPREFIX_MAX + 1] = {"
+	      "[INAT_LSTPFX_MAX + 1] = {"
 	for (i = 0; i < geid; i++)
 		for (j = 0; j < max_lprefix; j++)
 			if (etable[i,j])
@@ -325,7 +325,7 @@ END {
 	# print group opcode map's array
 	print "/* Group opcode map array */"
 	print "const insn_attr_t const *inat_group_tables[INAT_GRP_MAX + 1]"\
-	      "[INAT_LPREFIX_MAX + 1] = {"
+	      "[INAT_LSTPFX_MAX + 1] = {"
 	for (i = 0; i < ggid; i++)
 		for (j = 0; j < max_lprefix; j++)
 			if (gtable[i,j])