diff --git a/requirements/pip.txt b/requirements/pip.txt
index 1565fd594de..251e1a00122 100644
--- a/requirements/pip.txt
+++ b/requirements/pip.txt
@@ -73,7 +73,12 @@ stripe==1.20.2
 
 django-formtools==2.1
 django-dynamic-fixture==2.0.0
-docker==3.2.1
+
+# docker is pinned to 3.1.3 because we found some strange behavior
+# related to timeouts on EXEC with 3.2.1 that's not present with 3.1.3
+# https://github.com/rtfd/readthedocs.org/issues/3999
+docker==3.1.3
+
 django-textclassifier==1.0
 django-annoying==0.10.4
 django-messages-extends==0.6.0