diff --git a/disassembler/disassembler_x86.cc b/disassembler/disassembler_x86.cc
index e22542f..456e3b5 100644
--- a/disassembler/disassembler_x86.cc
+++ b/disassembler/disassembler_x86.cc
@@ -73,7 +73,7 @@
 
 enum RegFile { GPR, MMX, SSE };
 
-static void DumpAnyReg(std::ostream& os, uint8_t rex, uint8_t reg,
+static void DumpAnyReg(std::ostream& os, uint8_t rex, size_t reg,
                        bool byte_operand, uint8_t size_override, RegFile reg_file) {
   if (reg_file == GPR) {
     DumpReg0(os, rex, reg, byte_operand, size_override);