diff --git a/exonum_client/proofs/encoder.py b/exonum_client/proofs/encoder.py
index d0c1282..8e407a1 100644
--- a/exonum_client/proofs/encoder.py
+++ b/exonum_client/proofs/encoder.py
@@ -18,7 +18,7 @@ def _visit(entries: Dict[Any, Any]) -> None:
         for key, value in entries.items():
             if isinstance(value, dict):
                 _visit(value)
-            elif isinstance(value, list) and all(map(lambda x: 0 <= x <= 255, value)):
+            elif isinstance(value, list) and all(map(lambda x: 0 <= x <= 255 if isinstance(x, int) else False, value)):
                 obj_raw = bytes(value)
                 entries[key] = str(base64.b64encode(obj_raw), "utf-8")