diff --git a/webrtc/modules/rtp_rtcp/source/rtp_header_extension.cc b/webrtc/modules/rtp_rtcp/source/rtp_header_extension.cc
index 58b01bf410..64455ff3db 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_header_extension.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_header_extension.cc
@@ -39,7 +39,14 @@ int32_t RtpHeaderExtensionMap::Register(const RTPExtensionType type,
   std::map<uint8_t, HeaderExtension*>::iterator it =
       extensionMap_.find(id);
   if (it != extensionMap_.end()) {
-    return -1;
+    if (it->second->type != type) {
+      // An extension is already registered with the same id
+      // but a different type, so return failure.
+      return -1;
+    }
+    // This extension type is already registered with this id,
+    // so return success.
+    return 0;
   }
   extensionMap_[id] = new HeaderExtension(type);
   return 0;
@@ -52,9 +59,7 @@ int32_t RtpHeaderExtensionMap::Deregister(const RTPExtensionType type) {
   }
   std::map<uint8_t, HeaderExtension*>::iterator it =
       extensionMap_.find(id);
-  if (it == extensionMap_.end()) {
-    return -1;
-  }
+  assert(it != extensionMap_.end());
   delete it->second;
   extensionMap_.erase(it);
   return 0;
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_header_extension_unittest.cc b/webrtc/modules/rtp_rtcp/source/rtp_header_extension_unittest.cc
index e4160c7c51..e47902e5c5 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_header_extension_unittest.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_header_extension_unittest.cc
@@ -44,9 +44,16 @@ TEST_F(RtpHeaderExtensionTest, RegisterIllegalArg) {
   EXPECT_EQ(-1, map_.Register(kRtpExtensionTransmissionTimeOffset, 15));
 }
 
+TEST_F(RtpHeaderExtensionTest, Idempotent) {
+  EXPECT_EQ(0, map_.Register(kRtpExtensionTransmissionTimeOffset, kId));
+  EXPECT_EQ(0, map_.Register(kRtpExtensionTransmissionTimeOffset, kId));
+  EXPECT_EQ(0, map_.Deregister(kRtpExtensionTransmissionTimeOffset));
+  EXPECT_EQ(0, map_.Deregister(kRtpExtensionTransmissionTimeOffset));
+}
+
 TEST_F(RtpHeaderExtensionTest, NonUniqueId) {
   EXPECT_EQ(0, map_.Register(kRtpExtensionTransmissionTimeOffset, kId));
-  EXPECT_EQ(-1, map_.Register(kRtpExtensionTransmissionTimeOffset, kId));
+  EXPECT_EQ(-1, map_.Register(kRtpExtensionAudioLevel, kId));
 }
 
 TEST_F(RtpHeaderExtensionTest, GetTotalLength) {