diff --git a/src/thread_local_storage.real.ml b/src/thread_local_storage.real.ml
index 2d33f62c..250982ee 100644
--- a/src/thread_local_storage.real.ml
+++ b/src/thread_local_storage.real.ml
@@ -14,7 +14,7 @@ type 'a key = {
 let counter = Atomic.make 0
 
 (** Value used to detect a TLS slot that was not initialized yet *)
-let sentinel_value_for_uninit_tls_ () : Obj.t = Obj.repr counter
+let[@inline] sentinel_value_for_uninit_tls_ () : Obj.t = Obj.repr counter
 
 let new_key compute : _ key =
   let index = Atomic.fetch_and_add counter 1 in