diff --git a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
--- a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
+++ b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp
@@ -493,16 +493,15 @@
     insn->displacementSize = (insn->hasAdSize ? 2 : 4);
     insn->immediateSize = (insn->hasOpSize ? 2 : 4);
   } else if (insn->mode == MODE_64BIT) {
+    insn->displacementSize = 4;
     if (insn->rexPrefix && wFromREX(insn->rexPrefix)) {
       insn->registerSize = 8;
       insn->addressSize = (insn->hasAdSize ? 4 : 8);
-      insn->displacementSize = 4;
       insn->immediateSize = 4;
       insn->hasOpSize = false;
     } else {
       insn->registerSize = (insn->hasOpSize ? 2 : 4);
       insn->addressSize = (insn->hasAdSize ? 4 : 8);
-      insn->displacementSize = (insn->hasOpSize ? 2 : 4);
       insn->immediateSize = (insn->hasOpSize ? 2 : 4);
     }
   }
diff --git a/llvm/unittests/MC/X86/X86MCDisassemblerTest.cpp b/llvm/unittests/MC/X86/X86MCDisassemblerTest.cpp
--- a/llvm/unittests/MC/X86/X86MCDisassemblerTest.cpp
+++ b/llvm/unittests/MC/X86/X86MCDisassemblerTest.cpp
@@ -142,4 +142,10 @@
   checkBytes({0x49, 0xc7, 0x04, 0x24, 0xf5, 0xfe, 0xff, 0xff});
   checkOperand(0, 0, 4, 0);
   checkOperand(1, 0xfffffffffffffef5, 4, 4);
+
+  // mov    %ax, 0x1568179(%rbx)
+  // Test that the displacement operand size is not affected by the operand
+  // size override prefix.
+  checkBytes({0x66, 0x89, 0x83, 0x79, 0x81, 0x56, 0x01});
+  checkOperand(0, 0x1568179, 3, 4);
 }