diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index 665b9d0..dde21d5 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -835,7 +835,7 @@
 }
 
 static void do_for_partition(Transport* transport, const char *part, const char *slot,
-                             std::function<void(const std::string&)> func, bool force_slot) {
+                             const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
     std::string current_slot;
 
@@ -867,7 +867,7 @@
  * partition does not support slots.
  */
 static void do_for_partitions(Transport* transport, const char *part, const char *slot,
-                              std::function<void(const std::string&)> func, bool force_slot) {
+                              const std::function<void(const std::string&)>& func, bool force_slot) {
     std::string has_slot;
 
     if (slot && strcmp(slot, "all") == 0) {
diff --git a/fastboot/socket_test.cpp b/fastboot/socket_test.cpp
index affbdfd..373abc3 100644
--- a/fastboot/socket_test.cpp
+++ b/fastboot/socket_test.cpp
@@ -34,7 +34,7 @@
 // Creates connected sockets |server| and |client|. Returns true on success.
 bool MakeConnectedSockets(Socket::Protocol protocol, std::unique_ptr<Socket>* server,
                           std::unique_ptr<Socket>* client,
-                          const std::string hostname = "localhost") {
+                          const std::string& hostname = "localhost") {
     *server = Socket::NewServer(protocol, 0);
     if (*server == nullptr) {
         ADD_FAILURE() << "Failed to create server.";