diff --git a/advent.ipkg b/advent.ipkg
index 119b03c..607e26e 100644
--- a/advent.ipkg
+++ b/advent.ipkg
@@ -19,6 +19,7 @@ depends = base
         , tailrec
         , eff
         , elab-util
+        , sop
         , ansi
         , if-unsolved-implicit
         , c-ffi