diff --git a/src/app/rpmostree-dbus-helpers.c b/src/app/rpmostree-dbus-helpers.c
index 083c69a3..9a6a8fa4 100644
--- a/src/app/rpmostree-dbus-helpers.c
+++ b/src/app/rpmostree-dbus-helpers.c
@@ -489,6 +489,7 @@ rpmostree_transaction_get_response_sync (RPMOSTreeSysroot *sysroot_proxy,
   gint cancel_handler;
   gulong signal_handler = 0;
   gboolean success = FALSE;
+  gboolean just_started = FALSE;
 
   connection = g_dbus_proxy_get_connection (G_DBUS_PROXY (sysroot_proxy));
 
@@ -544,10 +545,21 @@ rpmostree_transaction_get_response_sync (RPMOSTreeSysroot *sysroot_proxy,
 
   /* Tell the server we're ready to receive signals. */
   if (!rpmostree_transaction_call_start_sync (transaction,
+                                              &just_started,
                                               cancellable,
                                               error))
     goto out;
 
+  /* FIXME Use the 'just_started' flag to determine whether to print
+   *       a message about reattaching to an in-progress transaction,
+   *       like:
+   *
+   *       Existing upgrade in progress, reattaching.  Control-C to cancel.
+   *
+   *       But that requires having a printable description of the
+   *       operation.  Maybe just add a string arg to this function?
+   */
+
   g_main_loop_run (tp->loop);
 
   g_cancellable_disconnect (cancellable, cancel_handler);
diff --git a/src/daemon/org.projectatomic.rpmostree1.xml b/src/daemon/org.projectatomic.rpmostree1.xml
index 1502ca90..10f25d54 100644
--- a/src/daemon/org.projectatomic.rpmostree1.xml
+++ b/src/daemon/org.projectatomic.rpmostree1.xml
@@ -106,8 +106,13 @@
     <!-- Yes, we can. -->
     <method name="Cancel"/>
 
-    <!-- For owner to call when ready to receive signals -->
-    <method name="Start"/>
+    <!-- For a client to call when ready to receive signals.
+         The return boolean indicates whether the transaction was
+         started by this method call (true) or was already started
+         by another client (false). -->
+    <method name="Start">
+      <arg type="b" name="started" direction="out"/>
+    </method>
 
     <signal name="Finished">
       <arg name="success" type="b" direction="out"/>
diff --git a/src/daemon/rpmostreed-transaction.c b/src/daemon/rpmostreed-transaction.c
index 56ad25c0..8aa3159f 100644
--- a/src/daemon/rpmostreed-transaction.c
+++ b/src/daemon/rpmostreed-transaction.c
@@ -506,6 +506,7 @@ transaction_handle_start (RPMOSTreeTransaction *transaction,
 {
   RpmostreedTransaction *self = RPMOSTREED_TRANSACTION (transaction);
   RpmostreedTransactionPrivate *priv = rpmostreed_transaction_get_private (self);
+  gboolean started = FALSE;
 
   /* The bus name watch ID doubles as a "not-yet-started" flag.
    * Once started the transaction proceeds independently of the
@@ -514,6 +515,8 @@ transaction_handle_start (RPMOSTreeTransaction *transaction,
     {
       GTask *task;
 
+      started = TRUE;
+
       g_debug ("%s (%p): Started", G_OBJECT_TYPE_NAME (self), self);
 
       g_bus_unwatch_name (priv->watch_id);
@@ -525,16 +528,9 @@ transaction_handle_start (RPMOSTreeTransaction *transaction,
                          NULL);
       g_task_run_in_thread (task, transaction_execute_thread);
       g_object_unref (task);
+    }
 
-      rpmostree_transaction_complete_start (transaction, invocation);
-    }
-  else
-    {
-      g_dbus_method_invocation_return_error (invocation,
-                                             RPM_OSTREED_ERROR,
-                                             RPM_OSTREED_ERROR_FAILED,
-                                             "Transaction has already started");
-    }
+  rpmostree_transaction_complete_start (transaction, invocation, started);
 
   return TRUE;
 }