diff --git a/doc/requirements.txt b/doc/requirements.txt
index 40acfd6..2250583 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,4 +1,5 @@
 numpy
 scipy
 pysolar>=0.9
-.
\ No newline at end of file
+python-dateutil
+.