diff --git a/requirements.txt b/requirements.txt
index 5c57d2c..2d37dce 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -8,7 +8,7 @@ python-multipart>=0.0.6
 PyYAML>=6.0
 asyncpg>=0.29.0
 markdown>=3.5.0
-# Core artdag from GitHub
-git+https://github.com/gilesbradshaw/art-dag.git
+# Core artdag from GitHub (pinned to include sexp module)
+git+https://github.com/gilesbradshaw/art-dag.git@db0c12c
 # Shared components
 git+https://git.rose-ash.com/art-dag/common.git@11aa056