diff --git a/requirements.txt b/requirements.txt
index 74226c8..fe2ca1e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -12,6 +12,7 @@ sphinx-prime-applets == 1.0.2
 sphinx-dropdown-toggle == 1.0.0
 sphinx-code-examples == 1.2.0
 sphinx-accessibility == 1.0.1
+teachbooks-sphinx-tippy == 1.0.13
 
 git+https://github.com/TeachBooks/Sphinx-Thebe