diff --git a/lightweight_mmm/plot.py b/lightweight_mmm/plot.py
index cd1c74f..8d9a101 100644
--- a/lightweight_mmm/plot.py
+++ b/lightweight_mmm/plot.py
@@ -805,6 +805,7 @@ def plot_media_channel_posteriors(
     channel_names = np.arange(np.shape(media_channel_posteriors)[1])
   fig, axes = plt.subplots(
       nrows=n_media_channels, ncols=n_geos, figsize=fig_size)
+  media_channel_posteriors = np.asarray(media_channel_posteriors)
   for channel_i, channel_axis in enumerate(axes):
     if isinstance(channel_axis, np.ndarray):
       for geo_i, geo_axis in enumerate(channel_axis):