diff --git a/openlibrary/core/lending.py b/openlibrary/core/lending.py
index 17f5a470582..acff7027927 100644
--- a/openlibrary/core/lending.py
+++ b/openlibrary/core/lending.py
@@ -462,10 +462,11 @@ def get_ocaid(item: dict) -> str | None:
         possible_fields.remove('ia')
         possible_fields.append('ia')
 
-    ocaids = []
+    ocaids: list[str] = []
     for field in possible_fields:
         if item.get(field):
-            ocaids += item[field] if isinstance(item[field], list) else [item[field]]
+            val = cast(list[str] | str, item[field])
+            ocaids += val if isinstance(val, list) else [val]
     ocaids = uniq(ocaids)
     return next((ocaid for ocaid in ocaids if not is_non_ia_ocaid(ocaid)), None)
 
diff --git a/openlibrary/core/vendors.py b/openlibrary/core/vendors.py
index 871732a38a9..2d7c1c2c050 100644
--- a/openlibrary/core/vendors.py
+++ b/openlibrary/core/vendors.py
@@ -587,8 +587,8 @@ def _get_betterworldbooks_metadata(isbn: str) -> dict | None:
             price = _price
             qlt = 'new'
 
-    market_price = ('$' + market_price[0]) if market_price else None
-    return betterworldbooks_fmt(isbn, qlt, price, market_price)
+    first_market_price = ('$' + market_price[0]) if market_price else None
+    return betterworldbooks_fmt(isbn, qlt, price, first_market_price)
 
 
 def betterworldbooks_fmt(
diff --git a/requirements_test.txt b/requirements_test.txt
index 908771821fd..3c166240e5d 100644
--- a/requirements_test.txt
+++ b/requirements_test.txt
@@ -4,7 +4,7 @@
 
 -r requirements.txt
 debugpy>=1.6.4
-mypy==1.11.2
+mypy==1.13.0
 pymemcache==4.0.0
 pytest==8.3.3
 pytest-asyncio==0.24.0