diff --git a/ablescript/src/interpret.rs b/ablescript/src/interpret.rs
index 49ebc9a..7d314be 100644
--- a/ablescript/src/interpret.rs
+++ b/ablescript/src/interpret.rs
@@ -523,18 +523,23 @@ impl<H: HostInterface> ExecEnv<H> {
                 .take(n_alternations)
                 .map(|chunk| ValueRef::clone(&chunk[0]))
                 .chain(
-                    args[2 * n_alternations..]
+                    args.get(2 * n_alternations..)
                         .iter()
+                        .copied()
+                        .flatten()
                         .map(ValueRef::clone)
                         .take(extra_l),
                 )
                 .collect(),
             args.chunks(2)
                 .take(n_alternations)
-                .map(|chunk| ValueRef::clone(&chunk[1]))
+                .flat_map(|chunk| chunk.get(1))
+                .map(ValueRef::clone)
                 .chain(
-                    args[2 * n_alternations..]
+                    args.get(2 * n_alternations..)
                         .iter()
+                        .copied()
+                        .flatten()
                         .map(ValueRef::clone)
                         .take(extra_r),
                 )