diff --git a/include/config.hpp b/include/config.hpp
index 3dd699ae..3490c3f1 100644
--- a/include/config.hpp
+++ b/include/config.hpp
@@ -35,7 +35,7 @@ class Config {
   void setupConfig(Json::Value &dst, const std::string &config_file, int depth);
   void resolveConfigIncludes(Json::Value &config, int depth);
   void mergeConfig(Json::Value &a_config_, Json::Value &b_config_);
-  std::optional<std::string> findIncludePath(const std::string name);
+  static std::optional<std::string> findIncludePath(const std::string &name);
 
   std::string config_file_;
 
diff --git a/src/config.cpp b/src/config.cpp
index 29a55e7c..5f14df5e 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -89,7 +89,7 @@ void Config::setupConfig(Json::Value &dst, const std::string &config_file, int d
   mergeConfig(dst, tmp_config);
 }
 
-std::optional<std::string> Config::findIncludePath(const std::string name) {
+std::optional<std::string> Config::findIncludePath(const std::string &name) {
   auto match1 = tryExpandPath(name, "");
   if (!match1.empty()) {
     return match1.front();