diff --git a/.github/workflows/checks.yml b/.github/workflows/checks.yml
index 70faf43..5011f5a 100644
--- a/.github/workflows/checks.yml
+++ b/.github/workflows/checks.yml
@@ -29,7 +29,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install black isort
+          python -m pip install black==24.* isort==5.*
 
       - name: Run "black --check"
         run: |
diff --git a/swagger_server/models/base_model_.py b/swagger_server/models/base_model_.py
index 703f3e0..d30aa67 100644
--- a/swagger_server/models/base_model_.py
+++ b/swagger_server/models/base_model_.py
@@ -40,9 +40,11 @@ def to_dict(self):
             elif isinstance(value, dict):
                 result[attr] = dict(
                     map(
-                        lambda item: (item[0], item[1].to_dict())
-                        if hasattr(item[1], "to_dict")
-                        else item,
+                        lambda item: (
+                            (item[0], item[1].to_dict())
+                            if hasattr(item[1], "to_dict")
+                            else item
+                        ),
                         value.items(),
                     )
                 )