diff --git a/src/pool/gen/mkshims.ml b/src/pool/gen/mkshims.ml
index 97c7745a..3154490a 100644
--- a/src/pool/gen/mkshims.ml
+++ b/src/pool/gen/mkshims.ml
@@ -1,6 +1,6 @@
 
 let atomic_before_412 = {|
-  type !'a t = {mutable x: 'a}
+  type 'a t = {mutable x: 'a}
   let[@inline] make x = {x}
   let[@inline] get {x} = x
   let[@inline] set r x = r.x <- x