diff --git a/{{cookiecutter.project_slug}}/pyproject.toml b/{{cookiecutter.project_slug}}/pyproject.toml
index a53e6c1f..31e290df 100644
--- a/{{cookiecutter.project_slug}}/pyproject.toml
+++ b/{{cookiecutter.project_slug}}/pyproject.toml
@@ -150,11 +150,20 @@ select = [
 ignore = [
   "S101", # Use of assert detected https://docs.astral.sh/ruff/rules/assert/
   "RUF012", # Mutable class attributes should be annotated with `typing.ClassVar`
-  "SIM102" # sometimes it's better to nest
+  "SIM102", # sometimes it's better to nest
+  "UP038" # Checks for uses of isinstance/issubclass that take a tuple 
+          # of types for comparison.
+          # Deactivated because it can make the code slow: 
+          # https://github.com/astral-sh/ruff/issues/7871
 ]
 # Allow fix for all enabled rules (when `--fix`) is provided.
 fixable = ["ALL"]
 unfixable = []
+# The fixes in extend-unsafe-fixes will require 
+# provide the `--unsafe-fixes` flag when fixing.
+extend-unsafe-fixes = [
+    "UP038"
+]
 # Allow unused variables when underscore-prefixed.
 dummy-variable-rgx = "^(_+|(_+[a-zA-Z0-9_]*[a-zA-Z0-9]+?))$"