diff --git a/src/java_lang_Class.cc b/src/java_lang_Class.cc
index 9d48ede..cba037a 100644
--- a/src/java_lang_Class.cc
+++ b/src/java_lang_Class.cc
@@ -218,7 +218,7 @@
 }
 
 Method* FindConstructorOrMethodInArray(ObjectArray<Method>* methods, String* name,
-    std::string& signature) {
+    const std::string& signature) {
   if (methods == NULL) {
     return NULL;
   }