diff --git a/crates/aiken-lang/src/uplc.rs b/crates/aiken-lang/src/uplc.rs
index 822202a7..15384e91 100644
--- a/crates/aiken-lang/src/uplc.rs
+++ b/crates/aiken-lang/src/uplc.rs
@@ -1205,7 +1205,9 @@ impl<'a> CodeGenerator<'a> {
                             indices: arguments_index
                                 .iter()
                                 .map(|(label, var_name, index)| {
-                                    let field_type = type_map.get(label).unwrap();
+                                    let field_type = type_map
+                                        .get(label)
+                                        .unwrap_or_else(|| type_map.get_index(*index).unwrap().1);
                                     (*index, var_name.clone(), field_type.clone())
                                 })
                                 .collect_vec(),
diff --git a/examples/acceptance_tests/055/aiken.lock b/examples/acceptance_tests/055/aiken.lock
new file mode 100644
index 00000000..00bfb887
--- /dev/null
+++ b/examples/acceptance_tests/055/aiken.lock
@@ -0,0 +1,13 @@
+# This file was generated by Aiken
+# You typically do not need to edit this file
+
+[[requirements]]
+name = "aiken-lang/stdlib"
+version = "cf89161cbcd5e2c9519e7ea5d61986473b708179"
+source = "github"
+
+[[packages]]
+name = "aiken-lang/stdlib"
+version = "cf89161cbcd5e2c9519e7ea5d61986473b708179"
+requirements = []
+source = "github"
diff --git a/examples/acceptance_tests/055/aiken.toml b/examples/acceptance_tests/055/aiken.toml
new file mode 100644
index 00000000..e1b10c5d
--- /dev/null
+++ b/examples/acceptance_tests/055/aiken.toml
@@ -0,0 +1,6 @@
+name = "aiken-lang/acceptance_test_036"
+version = "0.0.0"
+
+dependencies = [
+  { name = "aiken-lang/stdlib", version="cf89161cbcd5e2c9519e7ea5d61986473b708179", source = "github" },
+]
diff --git a/examples/acceptance_tests/055/lib/tests.ak b/examples/acceptance_tests/055/lib/tests.ak
new file mode 100644
index 00000000..482e6035
--- /dev/null
+++ b/examples/acceptance_tests/055/lib/tests.ak
@@ -0,0 +1,66 @@
+use aiken/bytearray
+use aiken/hash.{Hash, Sha2_256, sha2_256}
+use aiken/list
+use aiken/string
+
+//  MerkleTree in Aiken (ported from: https://github.com/input-output-hk/hydra/blob/master/plutus-merkle-tree/src/Plutus/MerkleTree.hs)
+
+pub type MerkleTree {
+  Empty
+  Leaf { hash: Hash<Sha2_256, ByteArray>, value: ByteArray }
+  Node { hash: Hash<Sha2_256, ByteArray>, left: MerkleTree, right: MerkleTree }
+}
+
+pub fn root_hash(t: MerkleTree) -> Hash<Sha2_256, ByteArray> {
+  when t is {
+    Empty -> #""
+    Leaf { hash, .. } -> hash
+    Node { hash, .. } -> hash
+  }
+}
+
+pub fn is_equal(a: MerkleTree, b: MerkleTree) -> Bool {
+  root_hash(a) == root_hash(b)
+}
+
+pub fn size(t: MerkleTree) -> Int {
+  when t is {
+    Empty -> 0
+    Leaf{..} -> 1
+    Node { left, right, .. } -> size(left) + size(right)
+  }
+}
+
+fn combine_hash(h1: Hash<alg, a>, h2: Hash<alg, a>) -> Hash<alg, a> {
+  sha2_256(bytearray.concat(h1, h2))
+}
+
+pub fn from_list(items0: List<ByteArray>) -> MerkleTree {
+  do_from_list(items0, list.length(items0))
+}
+
+fn do_from_list(items: List<ByteArray>, len: Int) -> MerkleTree {
+  when items is {
+    [] -> Empty
+    [value] -> Leaf { hash: sha2_256(value), value }
+    all -> {
+      let cutoff: Int = len / 2
+      let left =
+        all
+        |> list.take(cutoff)
+        |> do_from_list(cutoff)
+      let right =
+        all
+        |> list.drop(cutoff)
+        |> do_from_list(len - cutoff)
+      let hash = combine_hash(root_hash(left), root_hash(right))
+      Node { hash, left, right }
+    }
+  }
+}
+
+test foo() {
+  let items = [#"aa", #"bb", #"cc"]
+  let mt = from_list(items)
+  size(mt) == 3
+}