diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index b7dde603..b2b0ae7d 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -11,6 +11,7 @@ build:
   apt_packages:
     - libgeos-dev
     - libproj-dev
+    - libudunits2-dev
 
 sphinx:
   configuration: docs/source/conf.py