Index: lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
===================================================================
--- lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
+++ lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
@@ -961,8 +961,10 @@
       attrMask |= ATTR_XD;
   }
 
-  if (insn->rexPrefix & 0x08)
+  if (insn->rexPrefix & 0x08) {
     attrMask |= ATTR_REXW;
+    attrMask &= ~ATTR_ADSIZE;
+  }
 
   /*
    * JCXZ/JECXZ need special handling for 16-bit mode because the meaning
Index: test/MC/Disassembler/X86/x86-64.txt
===================================================================
--- test/MC/Disassembler/X86/x86-64.txt
+++ test/MC/Disassembler/X86/x86-64.txt
@@ -486,3 +486,9 @@
 
 # CHECK: nopq %rax
 0x48 0x0f 0x1f 0xC0
+
+# CHECK: popq    %r14
+0x67 0x49 0x5e
+
+# CHECK: pushq    %r14
+0x67 0x49 0x56