diff --git a/ci/requirements_rtd.txt b/ci/requirements_rtd.txt
index 897f9f25..380563e7 100644
--- a/ci/requirements_rtd.txt
+++ b/ci/requirements_rtd.txt
@@ -1,4 +1,5 @@
 numpy
+h5py
 fabio
 sphinx
 sphinxcontrib-programoutput