diff --git a/compiler/utils/assembler_test.h b/compiler/utils/assembler_test.h
index bb22fe5..5c6bf13 100644
--- a/compiler/utils/assembler_test.h
+++ b/compiler/utils/assembler_test.h
@@ -259,7 +259,7 @@
                                               std::string (AssemblerTest::*GetName1)(const Reg1&),
                                               std::string (AssemblerTest::*GetName2)(const Reg2&),
                                               std::string (AssemblerTest::*GetName3)(const Reg3&),
-                                              std::string fmt,
+                                              const std::string& fmt,
                                               int bias) {
     std::string str;
     std::vector<int64_t> imms = CreateImmediateValuesBits(abs(imm_bits), (imm_bits > 0));