diff --git a/media/base/fake_rtp.cc b/media/base/fake_rtp.cc
index 4f42821762..21322419e1 100644
--- a/media/base/fake_rtp.cc
+++ b/media/base/fake_rtp.cc
@@ -21,7 +21,7 @@ void CompareHeaderExtensions(const char* packet1,
                              size_t packet1_size,
                              const char* packet2,
                              size_t packet2_size,
-                             const std::vector<int> encrypted_headers,
+                             const std::vector<int>& encrypted_headers,
                              bool expect_equal) {
   // Sanity check: packets must be large enough to contain the RTP header and
   // extensions header.
diff --git a/media/base/fake_rtp.h b/media/base/fake_rtp.h
index 2fa37a1231..8a176038cb 100644
--- a/media/base/fake_rtp.h
+++ b/media/base/fake_rtp.h
@@ -295,7 +295,7 @@ void CompareHeaderExtensions(const char* packet1,
                              size_t packet1_size,
                              const char* packet2,
                              size_t packet2_size,
-                             std::vector<int> encrypted_headers,
+                             const std::vector<int>& encrypted_headers,
                              bool expect_equal);
 
 #endif  // MEDIA_BASE_FAKE_RTP_H_
diff --git a/pc/rtp_transmission_manager.cc b/pc/rtp_transmission_manager.cc
index 8e3eec6ceb..951d1c38e5 100644
--- a/pc/rtp_transmission_manager.cc
+++ b/pc/rtp_transmission_manager.cc
@@ -638,7 +638,7 @@ std::vector<RtpSenderInfo>* RtpTransmissionManager::GetLocalSenderInfos(
 const RtpSenderInfo* RtpTransmissionManager::FindSenderInfo(
     const std::vector<RtpSenderInfo>& infos,
     const std::string& stream_id,
-    const std::string sender_id) const {
+    const std::string& sender_id) const {
   for (const RtpSenderInfo& sender_info : infos) {
     if (sender_info.stream_id == stream_id &&
         sender_info.sender_id == sender_id) {
diff --git a/pc/rtp_transmission_manager.h b/pc/rtp_transmission_manager.h
index bff9b48267..209c8408de 100644
--- a/pc/rtp_transmission_manager.h
+++ b/pc/rtp_transmission_manager.h
@@ -50,7 +50,7 @@ namespace webrtc {
 struct RtpSenderInfo {
   RtpSenderInfo() : first_ssrc(0) {}
   RtpSenderInfo(const std::string& stream_id,
-                const std::string sender_id,
+                const std::string& sender_id,
                 uint32_t ssrc)
       : stream_id(stream_id), sender_id(sender_id), first_ssrc(ssrc) {}
   bool operator==(const RtpSenderInfo& other) {
@@ -184,7 +184,7 @@ class RtpTransmissionManager : public RtpSenderBase::SetStreamsObserver {
       cricket::MediaType media_type);
   const RtpSenderInfo* FindSenderInfo(const std::vector<RtpSenderInfo>& infos,
                                       const std::string& stream_id,
-                                      std::string sender_id) const;
+                                      const std::string& sender_id) const;
 
   // Return the RtpSender with the given track attached.
   rtc::scoped_refptr<RtpSenderProxyWithInternal<RtpSenderInternal>>