diff --git a/Dockerfile.sphinx b/Dockerfile.sphinx
index dfa24d5..fccc176 100644
--- a/Dockerfile.sphinx
+++ b/Dockerfile.sphinx
@@ -18,5 +18,6 @@ RUN apt-get update && \
         texlive-latex-extra \
         texlive-latex-recommended \
         texlive-xetex \
-        tzdata && \
+        tzdata \
+        xindy && \
     pip3 install six sphinx_rtd_theme