diff --git a/crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs b/crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs
index b5a7effc28..c5e1b38969 100644
--- a/crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs
+++ b/crates/ruff_linter/src/rules/flake8_bugbear/rules/mutable_argument_default.rs
@@ -68,6 +68,12 @@ use crate::{Edit, Fix, FixAvailability, Violation};
 /// ## Options
 /// - `lint.flake8-bugbear.extend-immutable-calls`
 ///
+/// ## Fix safety
+///
+/// This fix is marked as unsafe because it replaces the mutable default with `None`
+/// and initializes it in the function body, which may not be what the user intended,
+/// as described above.
+///
 /// ## References
 /// - [Python documentation: Default Argument Values](https://docs.python.org/3/tutorial/controlflow.html#default-argument-values)
 #[derive(ViolationMetadata)]