diff --git a/ipc/glue/RPCChannel.cpp b/ipc/glue/RPCChannel.cpp
index bab3cd345191..461c00a5fa2a 100644
--- a/ipc/glue/RPCChannel.cpp
+++ b/ipc/glue/RPCChannel.cpp
@@ -330,7 +330,7 @@ RPCChannel::MaybeUndeferIncall()
     RPC_ASSERT(mDeferred.top().rpc_remote_stack_depth_guess() <= stackDepth,
                "fatal logic error");
 
-    if (mDeferred.top().rpc_remote_stack_depth_guess() < stackDepth)
+    if (mDeferred.top().rpc_remote_stack_depth_guess() < RemoteViewOfStackDepth(stackDepth))
         return;
 
     // maybe time to process this message
@@ -435,6 +435,13 @@ RPCChannel::OnMaybeDequeueOne()
     return true;
 }
 
+size_t
+RPCChannel::RemoteViewOfStackDepth(size_t stackDepth) const
+{
+    AssertWorkerThread();
+    return stackDepth - mOutOfTurnReplies.size();
+}
+
 void
 RPCChannel::Incall(const Message& call, size_t stackDepth)
 {
@@ -445,14 +452,7 @@ RPCChannel::Incall(const Message& call, size_t stackDepth)
     // Race detection: see the long comment near
     // mRemoteStackDepthGuess in RPCChannel.h.  "Remote" stack depth
     // means our side, and "local" means other side.
-    //
-    // We compare the remote stack depth guess against the "remote
-    // view of stack depth" because of out-of-turn replies.  When we
-    // receive one, our actual RPC stack depth doesn't decrease, but
-    // the other side (that sent the reply) thinks it has.  So, just
-    // adjust down by the number of out-of-turn replies.
-    size_t remoteViewOfStackDepth = (stackDepth - mOutOfTurnReplies.size());
-    if (call.rpc_remote_stack_depth_guess() != remoteViewOfStackDepth) {
+    if (call.rpc_remote_stack_depth_guess() != RemoteViewOfStackDepth(stackDepth)) {
         // RPC in-calls have raced.
         // the "winner", if there is one, gets to defer processing of
         // the other side's in-call
diff --git a/ipc/glue/RPCChannel.h b/ipc/glue/RPCChannel.h
index 2c757f2c6607..451d50ff080e 100644
--- a/ipc/glue/RPCChannel.h
+++ b/ipc/glue/RPCChannel.h
@@ -207,6 +207,18 @@ protected:
      */
     bool OnMaybeDequeueOne();
 
+    /**
+     * The "remote view of stack depth" can be different than the
+     * actual stack depth when there are out-of-turn replies.  When we
+     * receive one, our actual RPC stack depth doesn't decrease, but
+     * the other side (that sent the reply) thinks it has.  So, the
+     * "view" returned here is |stackDepth| minus the number of
+     * out-of-turn replies.
+     *
+     * Only called from the worker thread.
+     */
+    size_t RemoteViewOfStackDepth(size_t stackDepth) const;
+
     void Incall(const Message& call, size_t stackDepth);
     void DispatchIncall(const Message& call);