diff -r 61a1bf9eb0ce -r 001739cb8d08 src/HOL/Tools/groebner.ML
--- a/src/HOL/Tools/groebner.ML	Thu May 18 15:34:01 2023 +0200
+++ b/src/HOL/Tools/groebner.ML	Thu May 18 17:21:29 2023 +0200
@@ -781,7 +781,7 @@
   in
     Simplifier.cert_simproc (Thm.theory_of_thm idl_sub) "poly_eq_simproc"
      {lhss = [Thm.term_of (Thm.lhs_of idl_sub)],
-      proc = fn _ => fn _ => proc}
+      proc = Morphism.entity (fn _ => fn _ => proc)}
   end;
 
 val poly_eq_ss =