diff --git a/tests/gmap.ref b/tests/gmap.ref
index a4d42549233b5c0153c1b455eb21f2651d09f7d4..8b1fa98fcf41db2dd1a8077a4957ed1ff9032285 100644
--- a/tests/gmap.ref
+++ b/tests/gmap.ref
@@ -70,3 +70,9 @@ Failed to progress.
   
   ============================
   bool_decide (∅ ⊆ {[1; 2; 3]}) = true
+The command has indeed failed with message:
+Nothing to inject.
+The command has indeed failed with message:
+Nothing to inject.
+The command has indeed failed with message:
+Failed to progress.
diff --git a/tests/gmap.v b/tests/gmap.v
index 6cb7029b63ea9553c3255497fe63bd09b68fb38d..987c0fe699f9c45b55eb46191ac38d0721faeb2e 100644
--- a/tests/gmap.v
+++ b/tests/gmap.v
@@ -68,3 +68,17 @@ Proof.
   Show.
   reflexivity.
 Qed.
+
+Lemma should_not_unfold (m1 m2 : gmap nat nat) k x :
+  dom (gset nat) m1 = dom (gset nat) m2 →
+  <[k:=x]> m1 = <[k:=x]> m2 →
+  True.
+Proof.
+  (** Make sure that [injection]/[simplify_eq] does not unfold constructs on
+  [gmap] and [gset]. *)
+  intros Hdom Hinsert.
+  Fail injection Hdom.
+  Fail injection Hinsert.
+  Fail progress simplify_eq.
+  done.
+Qed.