diff --git a/tests/instance_merge_with_distinct_param.v b/tests/instance_merge_with_distinct_param.v
new file mode 100644
index 00000000..682f4476
--- /dev/null
+++ b/tests/instance_merge_with_distinct_param.v
@@ -0,0 +1,26 @@
+From HB Require Import structures.
+
+HB.mixin Record m1 T := { default1 : T }.
+
+HB.mixin Record m2 T := { default2 : T }.
+
+HB.structure Definition s1 := { T of m1 T }.
+HB.structure Definition s2 := { T of m2 T }.
+
+HB.instance Definition _ (X : s1.type) : m1 (list X) :=
+  m1.Build (list X) (cons default1 nil).
+HB.instance Definition list_m2 (X : s2.type) : m2 (list X) :=
+  m2.Build (list X) (cons default2 nil).
+
+HB.structure Definition s3 := { T of m1 T & m2 T }.
+
+HB.about list. (* should have s3 *)
+
+(* The s3 instance on list should be synthetized automatically, *)
+(* this is nontrivial because the parameters are not the same *)
+(* but there is a join in the hierarchy, so it can be defined. *)
+(* Actually just recalling the list_s2 instance above suffices. *)
+HB.instance Definition _ (X : s3.type) := list_m2 X.
+HB.about list.
+
+
diff --git a/tests/instance_merge_with_param.v b/tests/instance_merge_with_param.v
new file mode 100644
index 00000000..9fbc0759
--- /dev/null
+++ b/tests/instance_merge_with_param.v
@@ -0,0 +1,26 @@
+From HB Require Import structures.
+
+HB.mixin Record m1 T := { default1 : T }.
+
+HB.mixin Record m2 T := { default2 : T }.
+
+HB.structure Definition s1 := { T of m1 T }.
+HB.structure Definition s2 := { T of m2 T }.
+
+HB.instance Definition _ (X : s1.type) : m1 (list X) :=
+  m1.Build (list X) (cons default1 nil).
+HB.instance Definition list_m2 (X : s1.type) : m2 (list X) :=
+  m2.Build (list X) nil.
+
+HB.structure Definition s3 := { T of m1 T & m2 T }.
+
+HB.about list. (* should have s3 *)
+
+(* The s3 instance on list should be synthetized automatically, *)
+(* But since it's defined afterwards, it's not taken into account. *)
+(* The subtelty now is that there is a parameter, but it's always the same *)
+(* A simple recall suffices: *)
+HB.instance Definition _ (X : s1.type) := list_m2 X.
+HB.about list.
+
+