diff --git a/lib/Target/X86/X86Instr64bit.td b/lib/Target/X86/X86Instr64bit.td
index a3750a94605..b7d3b4b9c82 100644
--- a/lib/Target/X86/X86Instr64bit.td
+++ b/lib/Target/X86/X86Instr64bit.td
@@ -1313,7 +1313,8 @@ def BT64mr : RI<0xA3, MRMDestMem, (outs), (ins i64mem:$src1, GR64:$src2),
 
 def BT64ri8 : Ii8<0xBA, MRM4r, (outs), (ins GR64:$src1, i64i8imm:$src2),
                 "bt{q}\t{$src2, $src1|$src1, $src2}",
-                [(set EFLAGS, (X86bt GR64:$src1, i64immSExt8:$src2))]>, TB;
+                [(set EFLAGS, (X86bt GR64:$src1, i64immSExt8:$src2))]>, TB,
+		REX_W;
 // Note that these instructions don't need FastBTMem because that
 // only applies when the other operand is in a register. When it's
 // an immediate, bt is still fast.
diff --git a/test/MC/AsmParser/X86/x86_64-new-encoder.s b/test/MC/AsmParser/X86/x86_64-new-encoder.s
index 6cd22d03051..6988110be2d 100644
--- a/test/MC/AsmParser/X86/x86_64-new-encoder.s
+++ b/test/MC/AsmParser/X86/x86_64-new-encoder.s
@@ -126,3 +126,8 @@ movl	0, %eax   // CHECK: movl 0, %eax # encoding: [0x8b,0x04,0x25,A,A,A,A]
 // CHECK: jne
 // CHECK: encoding: [0x75,A]
         jnz 0
+
+// rdar://8017515
+btq $0x01,%rdx
+// CHECK: btq	$1, %rdx
+// CHECK:  encoding: [0x48,0x0f,0xba,0xe2,0x01]