diff --git a/src/client/opamConfigCommand.ml b/src/client/opamConfigCommand.ml
index 47c426f3b53..733498eb9ca 100644
--- a/src/client/opamConfigCommand.ml
+++ b/src/client/opamConfigCommand.ml
@@ -135,7 +135,7 @@ let print_bindingss_env output env =
   let rec aux = function
     | [] -> ()
     | (k, v, _) :: r ->
-      if not (List.exists (fun (k1, _, _) -> k = k1) r) then
+      if not (List.exists (fun (k1, _, _) -> (k : string) = (k1 : string)) r) then
         Printf.ksprintf output "%s=%s\n" k v;
       aux r
   in