diff --git a/bloom/internal/bitvec/bitvec.mbt b/bloom/internal/bitvec/bitvec.mbt
index 6505221..cd9cd1f 100644
--- a/bloom/internal/bitvec/bitvec.mbt
+++ b/bloom/internal/bitvec/bitvec.mbt
@@ -369,8 +369,10 @@ pub fn BitVector::unmarshal_bytes(bytes : Bytes) -> BitVector {
   let tail_mask = bytes[4:12].to_uint64_le()
   let words_needed = words_needed(length)
   let data = Array::make(words_needed, 0UL)
+  let mut offset = 12
   for i in 0..<words_needed {
-    data[i] = bytes[12 + i:20 + i].to_uint64_le()
+    data[i] = bytes[offset:offset + 8].to_uint64_le()
+    offset += 8
   }
   { length, tail_mask, data }
 }
diff --git a/bloom/internal/bitvec/bitvec_test.mbt b/bloom/internal/bitvec/bitvec_test.mbt
index 013e00d..5fdb975 100644
--- a/bloom/internal/bitvec/bitvec_test.mbt
+++ b/bloom/internal/bitvec/bitvec_test.mbt
@@ -270,3 +270,12 @@ test "serialization_roundtrip" {
   let deserialized = BitVector::from_string(serialized)
   assert_eq(original.to_string(), deserialized.to_string())
 }
+
+test "marshal_unmarshal_bytes_roundtrip_multiword" {
+  let original = BitVector::ones(128)
+  // Modify the second word so the bug cannot be masked by identical bytes
+  original.clear(64)
+  let serialized = original.marshal_bytes()
+  let deserialized = BitVector::unmarshal_bytes(serialized)
+  assert_eq(original.equal(deserialized), true)
+}