diff --git a/docs/environment.yml b/docs/environment.yml
index 5a3332b27..06ffdb0da 100644
--- a/docs/environment.yml
+++ b/docs/environment.yml
@@ -3,6 +3,7 @@ channels:
 - dean0x7d
 - defaults
 dependencies:
+- python==3.5
 - doxygen
 - pip
 - pip: