diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 9d46d06e01dd147fda13e0159958be115c3bc577..4c6b9a2d90e541542b5e2023c0a5ee7aab6e6a0d 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -69,6 +69,9 @@ jobs:
                 python euler/acoustic_pulse.py --lazy
                 python euler/vortex.py --oi --lazy
 
+                # --oversubscribe is an option for Open MPI (which is what the CI uses)
+                # It allows the CI to succeed even if the CI runner does not
+                # have a sufficient number of cores.
                 mpiexec -np 2 --oversubscribe python wave/wave-op-mpi.py --lazy
 
     docs: