diff --git a/.rtd-environment.yml b/.rtd-environment.yml
index e6f62b8..4091a26 100644
--- a/.rtd-environment.yml
+++ b/.rtd-environment.yml
@@ -6,6 +6,7 @@ dependencies:
   - mpi4py
   - six
   - joblib
+  - matplotlib
   - pip:
     - alabaster
     - emcee