diff --git a/include/utils/string.hpp b/include/utils/string.hpp
index a278e04f..fcb58b91 100644
--- a/include/utils/string.hpp
+++ b/include/utils/string.hpp
@@ -28,7 +28,7 @@ namespace string_util {
   string ltrim(const string& haystack, char needle);
   string rtrim(const string& haystack, char needle);
   string trim(const string& haystack, char needle);
-  string join(vector<string> strs, string delim);
+  string join(const vector<string>& strs, const string& delim);
   vector<string>& split_into(const string& s, char delim, vector<string>& container);
   vector<string> split(const string& s, char delim);
   size_t find_nth(const string& haystack, size_t pos, const string& needle, size_t nth);
diff --git a/src/utils/string.cpp b/src/utils/string.cpp
index 4fae58c0..0fe88f10 100644
--- a/src/utils/string.cpp
+++ b/src/utils/string.cpp
@@ -164,10 +164,10 @@ namespace string_util {
   /**
    * Join all strings in vector into a single string separated by delim
    */
-  string join(vector<string> strs, string delim) {
+  string join(const vector<string>& strs, const string& delim) {
     string str;
     for (auto& s : strs) {
-      str.append((str.empty() ? "" : move(delim)) + s);
+      str += (str.empty() ? "" : delim) + s;
     }
     return str;
   }