diff --git a/lib/src/local_working_copy.rs b/lib/src/local_working_copy.rs
index 3d80850ce..55a66f7be 100644
--- a/lib/src/local_working_copy.rs
+++ b/lib/src/local_working_copy.rs
@@ -836,7 +836,7 @@ impl TreeState {
 
     #[instrument(skip_all)]
     fn make_fsmonitor_matcher(
-        &mut self,
+        &self,
         fsmonitor_kind: Option<FsmonitorKind>,
     ) -> Result<FsmonitorMatcher, SnapshotError> {
         let (watchman_clock, changed_files) = match fsmonitor_kind {