diff --git a/mne/viz/_brain/_brain.py b/mne/viz/_brain/_brain.py
index 795fa424771..93554206f1b 100644
--- a/mne/viz/_brain/_brain.py
+++ b/mne/viz/_brain/_brain.py
@@ -1136,7 +1136,7 @@ def _configure_vertex_time_course(self):
         rms = np.linalg.norm(y, axis=0) / np.sqrt(len(y))
         del y
 
-        self.rms = self.mpl_canvas.axes.plot(
+        self.rms, = self.mpl_canvas.axes.plot(
             self._data['time'], rms,
             lw=3, label='RMS', zorder=3, color=self._fg_color,
             alpha=0.5, ls=':')