diff --git a/hugr/src/hugr/validate.rs b/hugr/src/hugr/validate.rs
index 30a7dce099..533a7e97d7 100644
--- a/hugr/src/hugr/validate.rs
+++ b/hugr/src/hugr/validate.rs
@@ -98,6 +98,11 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
         // Hierarchy and children. No type variables declared outside the root.
         self.validate_subtree(self.hugr.root(), &[])?;
 
+        #[cfg(test)]
+        {
+            crate::hugr::serialize::test::check_hugr_roundtrip(&self.hugr);
+        }
+
         Ok(())
     }