diff --git a/src/autobigs/engine/analysis/aligners.py b/src/autobigs/engine/analysis/aligners.py
index e680c79..a449c5a 100644
--- a/src/autobigs/engine/analysis/aligners.py
+++ b/src/autobigs/engine/analysis/aligners.py
@@ -39,8 +39,8 @@ class AsyncPairwiseAlignmentEngine(AbstractContextManager):
         return PairwiseAlignment(
             top_alignment.sequences[0],
             top_alignment.sequences[1],
-            top_alignment.indices[0],
-            top_alignment.indices[1],
+            tuple(top_alignment.indices[0]),
+            tuple(top_alignment.indices[1]),
             AlignmentStats(
                 percent_identity=top_alignment_identities/top_alignment.length,
                 mismatches=top_alignment_mismatches,
diff --git a/src/autobigs/engine/structures/alignment.py b/src/autobigs/engine/structures/alignment.py
index 8cfc8f9..c40b857 100644
--- a/src/autobigs/engine/structures/alignment.py
+++ b/src/autobigs/engine/structures/alignment.py
@@ -1,5 +1,6 @@
 from dataclasses import dataclass
 from numbers import Number
+from typing import Sequence
 
 @dataclass(frozen=True)
 class AlignmentStats:
@@ -12,6 +13,6 @@ class AlignmentStats:
 class PairwiseAlignment:
     reference: str
     query: str
-    reference_indices: list[Number]
-    query_indices: list[Number]
+    reference_indices: Sequence[Number]
+    query_indices: Sequence[Number]
     alignment_stats: AlignmentStats
\ No newline at end of file