Index: lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
===================================================================
--- lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
+++ lib/Target/X86/Disassembler/X86DisassemblerDecoder.cpp
@@ -980,6 +980,46 @@
       insn->opcode == 0xE3)
     attrMask ^= ATTR_ADSIZE;
 
+  /*
+   * In 64-bit mode all f64 superscripted opcodes ignore opcode size prefix
+   * In the current implementation, CALL/JMP/JCC instructions need to ignore 0x66
+   * this implements correct disassembly and consumes all 4 bytes of the immediate/displacement
+   * NOTE: intel spec states that all rel16 with f64 superscripts are Not Supported in 64-bit mode
+   */
+
+  if (insn->mode == MODE_64BIT && isPrefixAtLocation(insn, 0x66, insn->necessaryPrefixLocation)){
+    switch (insn->opcode){
+    case 0xE8:
+    case 0xE9:
+      if (insn-> opcodeType == ONEBYTE){ // breaks psubsb and other mmx instructions otherwise
+        attrMask ^= ATTR_OPSIZE;
+        insn->immediateSize = 4;
+        insn->displacementSize = 4;
+      }
+      break;
+    case 0x82:
+    case 0x83:
+    case 0x84:
+    case 0x85:
+    case 0x86:
+    case 0x87:
+    case 0x88:
+    case 0x89:
+    case 0x8A:
+    case 0x8B:
+    case 0x8C:
+    case 0x8D:
+    case 0x8E:
+    case 0x8F:
+      if (insn-> opcodeType == TWOBYTE){ // breaks lea and three byte ops otherwise
+        attrMask ^= ATTR_OPSIZE;
+        insn->immediateSize = 4;
+        insn->displacementSize = 4; // otherwise not sign extended, for some reason
+      }
+      break;
+    }
+  }
+
   if (getIDWithAttrMask(&instructionID, insn, attrMask))
     return -1;
 
Index: test/MC/Disassembler/X86/x86-64.txt
===================================================================
--- test/MC/Disassembler/X86/x86-64.txt
+++ test/MC/Disassembler/X86/x86-64.txt
@@ -301,3 +301,114 @@
 
 # CHECK: movq %rax, 1515870810
 0x67, 0x48 0xa3 0x5a 0x5a 0x5a 0x5a
+
+# CHECK: callq -32769
+0x66 0xe8 0xff 0x7f 0xff 0xff
+
+# CHECK: callq -32769
+0x66 0x66 0x48 0xe8 0xff 0x7f 0xff 0xff
+
+# CHECK: jmp -32769
+0xe9 0xff 0x7f 0xff 0xff
+
+# CHECK: jmp -32769
+0x66 0xe9 0xff 0x7f 0xff 0xff
+
+# CHECK: jmp -32769
+0x66 0x66 0x48 0xe9 0xff 0x7f 0xff 0xff
+
+# CHECK: jb -32769
+0x0f 0x82 0xff 0x7f 0xff 0xff
+
+# CHECK: jb -32769
+0x66 0x0f 0x82 0xff 0x7f 0xff 0xff
+
+# CHECK: jae -32769
+0x0f 0x83 0xff 0x7f 0xff 0xff
+
+# CHECK: jae -32769
+0x66 0x0f 0x83 0xff 0x7f 0xff 0xff
+
+# CHECK: je -32769
+0x0f 0x84 0xff 0x7f 0xff 0xff
+
+# CHECK: je -32769
+0x66 0x0f 0x84 0xff 0x7f 0xff 0xff
+
+# CHECK: jne -32769
+0x0f 0x85 0xff 0x7f 0xff 0xff
+
+# CHECK: jne -32769
+0x66 0x0f 0x85 0xff 0x7f 0xff 0xff
+
+# CHECK: jbe -32769
+0x0f 0x86 0xff 0x7f 0xff 0xff
+
+# CHECK: jbe -32769
+0x66 0x0f 0x86 0xff 0x7f 0xff 0xff
+
+# CHECK: ja -32769
+0x0f 0x87 0xff 0x7f 0xff 0xff
+
+# CHECK: ja -32769
+0x66 0x0f 0x87 0xff 0x7f 0xff 0xff
+
+# CHECK: js -32769
+0x0f 0x88 0xff 0x7f 0xff 0xff
+
+# CHECK: js -32769
+0x66 0x0f 0x88 0xff 0x7f 0xff 0xff
+
+# CHECK: jns -32769
+0x0f 0x89 0xff 0x7f 0xff 0xff
+
+# CHECK: jns -32769
+0x66 0x0f 0x89 0xff 0x7f 0xff 0xff
+
+# CHECK: jp -32769
+0x0f 0x8a 0xff 0x7f 0xff 0xff
+
+# CHECK: jp -32769
+0x66 0x0f 0x8a 0xff 0x7f 0xff 0xff
+
+# CHECK: jnp -32769
+0x0f 0x8b 0xff 0x7f 0xff 0xff
+
+# CHECK: jnp -32769
+0x66 0x0f 0x8b 0xff 0x7f 0xff 0xff
+
+# CHECK: jl -32769
+0x0f 0x8c 0xff 0x7f 0xff 0xff
+
+# CHECK: jl -32769
+0x66 0x0f 0x8c 0xff 0x7f 0xff 0xff
+
+# CHECK: jge -32769
+0x0f 0x8d 0xff 0x7f 0xff 0xff
+
+# CHECK: jge -32769
+0x66 0x0f 0x8d 0xff 0x7f 0xff 0xff
+
+# CHECK: jle -32769
+0x0f 0x8e 0xff 0x7f 0xff 0xff
+
+# CHECK: jle -32769
+0x66 0x0f 0x8e 0xff 0x7f 0xff 0xff
+
+# CHECK: jg -32769
+0x0f 0x8f 0xff 0x7f 0xff 0xff
+
+# CHECK: jg -32769
+0x66 0x0f 0x8f 0xff 0x7f 0xff 0xff
+
+# CHECK: lcallw	*-32769(%rip)
+0x66 0xff 0x1d 0xff 0x7f 0xff 0xff
+
+# CHECK: ljmpw	*-32769(%rip)
+0x66 0xff 0x2d 0xff 0x7f 0xff 0xff
+
+# CHECK: psubsb	(%rdx), %mm3
+0x0f 0xe8 0x1a
+
+# CHECK: psubsb	(%rdx), %xmm3
+0x66 0x0f 0xe8 0x1a