diff --git a/ipc/glue/MessageChannel.cpp b/ipc/glue/MessageChannel.cpp
index 655f51e4844..9f14a7b7bbc 100644
--- a/ipc/glue/MessageChannel.cpp
+++ b/ipc/glue/MessageChannel.cpp
@@ -753,7 +753,7 @@ MessageChannel::Send(Message* aMsg)
 {
     if (aMsg->capacity() >= kMinTelemetryMessageSize) {
         Telemetry::Accumulate(Telemetry::IPC_MESSAGE_SIZE,
-                              nsCString(aMsg->name()), aMsg->capacity());
+                              nsDependentCString(aMsg->name()), aMsg->capacity());
     }
 
     CxxStackFrame frame(*this, OUT_MESSAGE, aMsg);
@@ -1042,7 +1042,7 @@ MessageChannel::Send(Message* aMsg, Message* aReply)
 {
     if (aMsg->capacity() >= kMinTelemetryMessageSize) {
         Telemetry::Accumulate(Telemetry::IPC_MESSAGE_SIZE,
-                              nsCString(aMsg->name()), aMsg->capacity());
+                              nsDependentCString(aMsg->name()), aMsg->capacity());
     }
 
     nsAutoPtr<Message> msg(aMsg);
@@ -1227,6 +1227,10 @@ MessageChannel::Send(Message* aMsg, Message* aReply)
     MOZ_RELEASE_ASSERT(reply->is_sync());
 
     *aReply = Move(*reply);
+    if (aReply->capacity() >= kMinTelemetryMessageSize) {
+        Telemetry::Accumulate(Telemetry::IPC_REPLY_SIZE,
+                              nsDependentCString(aReply->name()), aReply->capacity());
+    }
     return true;
 }
 
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index f91f646ff04..b416c3ddb14 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -10428,6 +10428,16 @@
     "keyed": true,
     "description": "Measures the size of IPC messages by message name"
   },
+  "IPC_REPLY_SIZE": {
+    "alert_emails": ["wmccloskey@mozilla.com"],
+    "bug_numbers": [1264820],
+    "expires_in_version": "55",
+    "kind": "exponential",
+    "high": 8000000,
+    "n_buckets": 50,
+    "keyed": true,
+    "description": "Measures the size of IPC messages by message name"
+  },
   "MESSAGE_MANAGER_MESSAGE_SIZE": {
     "alert_emails": ["wmccloskey@mozilla.com"],
     "bug_numbers": [1260908],