diff --git a/openquake/hazardlib/calc/gmf.py b/openquake/hazardlib/calc/gmf.py
index <HASH>..<HASH> 100644
--- a/openquake/hazardlib/calc/gmf.py
+++ b/openquake/hazardlib/calc/gmf.py
@@ -279,7 +279,7 @@ class GmfComputer(object):
                 if len(intra_res.shape) == 1:  # a vector
                     intra_res = intra_res[:, None]
 
-            inter_res = tau * epsilons
+            inter_res = tau * epsilons  # shape (N, 1) * E => (N, E)
             gmf = to_imt_unit_values(mean + intra_res + inter_res, imt)
             stdi = tau.max(axis=0)  # from shape (N, E) => E
         return gmf, stdi, epsilons
Added comment [ci skip]