Index: lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
===================================================================
--- lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
+++ lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
@@ -758,6 +758,10 @@
 
       insn->opcodeType = TWOBYTE;
     }
+  } else if (current == 0xce && (insn->mode == MODE_64BIT)) {
+    // TODO: Do we need real error diagnostic in disassembler?
+    dbgprintf(insn, "Invalid instruction 'into' in 64-bit mode");
+    return -1;
   }
 
   /*
Index: test/MC/Disassembler/X86/x86-64-err.txt
===================================================================
--- test/MC/Disassembler/X86/x86-64-err.txt
+++ test/MC/Disassembler/X86/x86-64-err.txt
@@ -0,0 +1,6 @@
+# RUN: llvm-mc --disassemble %s -triple=x86_64 2>&1 | FileCheck --check-prefix=64 %s
+# RUN: llvm-mc --disassemble %s -triple=i386 | FileCheck --check-prefix=32 %s
+
+# 64: warning: invalid instruction encoding
+# 32: into
+0xce