diff --git a/spack-environment/packages.yaml b/spack-environment/packages.yaml
index e0103970b6cd7ff0713c5f250232f0bd1eb44677..99b670698336ef9175332f45391c8b9468aac1b2 100644
--- a/spack-environment/packages.yaml
+++ b/spack-environment/packages.yaml
@@ -125,6 +125,7 @@ packages:
   graphviz:
     require:
     - '@8.0.1'
+    - +expat
   hepmc3:
     require:
     - '@3.2.6'