diff --git a/src/library/tactic/class_instance_synth.cpp b/src/library/tactic/class_instance_synth.cpp
index 8405968a1..fba4e3473 100644
--- a/src/library/tactic/class_instance_synth.cpp
+++ b/src/library/tactic/class_instance_synth.cpp
@@ -236,9 +236,15 @@ struct class_instance_elaborator : public choice_iterator {
                 type = tc.whnf(type).first;
                 if (!is_pi(type))
                     break;
-                pair<expr, constraint> ac = mk_class_instance_elaborator(m_C, m_ctx, some_expr(binding_domain(type)), g, m_depth+1);
-                expr arg = ac.first;
-                cs.push_back(ac.second);
+                expr arg;
+                if (binding_info(type).is_inst_implicit()) {
+                    pair<expr, constraint> ac = mk_class_instance_elaborator(m_C, m_ctx, some_expr(binding_domain(type)),
+                                                                             g, m_depth+1);
+                    arg = ac.first;
+                    cs.push_back(ac.second);
+                } else {
+                    arg = m_ctx.mk_meta(m_C->m_ngen, some_expr(binding_domain(type)), g);
+                }
                 r    = mk_app(r, arg, g);
                 type = instantiate(binding_body(type), arg);
             }
diff --git a/tests/lean/run/algebra1.lean b/tests/lean/run/algebra1.lean
index 457abe94a..628e4209e 100644
--- a/tests/lean/run/algebra1.lean
+++ b/tests/lean/run/algebra1.lean
@@ -65,7 +65,7 @@ namespace semigroup
   definition assoc  {A : Type} (s : semigroup_struct A) : is_assoc (mul s)
   := semigroup_struct.rec (fun f h, h) s
 
-  definition is_mul_struct  [instance] (A : Type) (s : semigroup_struct A) : mul_struct A
+  definition is_mul_struct  [instance] (A : Type) [s : semigroup_struct A] : mul_struct A
   := mul_struct.mk (mul s)
 
   inductive semigroup : Type :=
@@ -74,7 +74,7 @@ namespace semigroup
   definition carrier  [coercion] (g : semigroup)
   := semigroup.rec (fun c s, c) g
 
-  definition is_semigroup  [instance] (g : semigroup) : semigroup_struct (carrier g)
+  definition is_semigroup  [instance] [g : semigroup] : semigroup_struct (carrier g)
   := semigroup.rec (fun c s, s) g
 end semigroup
 
@@ -91,7 +91,7 @@ namespace monoid
   := monoid_struct.rec (fun mul id a i, a) s
 
   open semigroup
-  definition is_semigroup_struct  [instance] (A : Type) (s : monoid_struct A) : semigroup_struct A
+  definition is_semigroup_struct  [instance] (A : Type) [s : monoid_struct A] : semigroup_struct A
   := semigroup_struct.mk (mul s) (assoc s)
 
   inductive monoid : Type :=
diff --git a/tests/lean/run/class7.lean b/tests/lean/run/class7.lean
index 4b6c248e7..ae001064f 100644
--- a/tests/lean/run/class7.lean
+++ b/tests/lean/run/class7.lean
@@ -9,7 +9,7 @@ theorem inh_bool [instance] : inh Prop
 
 set_option class.trace_instances true
 
-theorem inh_fun [instance] {A B : Type} (H : inh B) : inh (A → B)
+theorem inh_fun [instance] {A B : Type} [H : inh B] : inh (A → B)
 := inh.rec (λ b, inh.intro (λ a : A, b)) H
 
 theorem tst {A B : Type} (H : inh B) : inh (A → B → B)
diff --git a/tests/lean/run/class8.lean b/tests/lean/run/class8.lean
index 2982e5679..fb3e3fd02 100644
--- a/tests/lean/run/class8.lean
+++ b/tests/lean/run/class8.lean
@@ -15,10 +15,10 @@ theorem inh_exists {A : Type} {P : A → Prop} (H : ∃x, P x) : inh A
 theorem inh_bool [instance] : inh Prop
 := inh.intro true
 
-theorem inh_fun [instance] {A B : Type} (H : inh B) : inh (A → B)
+theorem inh_fun [instance] {A B : Type} [H : inh B] : inh (A → B)
 := inh.rec (λb, inh.intro (λa : A, b)) H
 
-theorem pair_inh [instance] {A : Type} {B : Type} (H1 : inh A) (H2 : inh B) : inh (prod A B)
+theorem pair_inh [instance] {A : Type} {B : Type} [H1 : inh A] [H2 : inh B] : inh (prod A B)
 := inh_elim H1 (λa, inh_elim H2 (λb, inh.intro (pair a b)))
 
 definition assump := eassumption
diff --git a/tests/lean/run/elab_bug1.lean b/tests/lean/run/elab_bug1.lean
index e1421fffa..9afb4341d 100644
--- a/tests/lean/run/elab_bug1.lean
+++ b/tests/lean/run/elab_bug1.lean
@@ -42,19 +42,19 @@ theorem congr_const_iff [instance] (T1 : Type) (R1 : T1 → T1 → Prop) (c : Pr
   congruence R1 iff (const T1 c) := congr_const iff iff.refl T1 R1 c
 
 theorem congr_or [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
+    [H1 : congruence R iff f1] [H2 : congruence R iff f2] :
   congruence R iff (λx, f1 x ∨ f2 x) := sorry
 
 theorem congr_implies [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
+    [H1 : congruence R iff f1] [H2 : congruence R iff f2] :
   congruence R iff (λx, f1 x → f2 x) := sorry
 
 theorem congr_iff [instance] (T : Type) (R : T → T → Prop) (f1 f2 : T → Prop)
-    (H1 : congruence R iff f1) (H2 : congruence R iff f2) :
+    [H1 : congruence R iff f1] [H2 : congruence R iff f2] :
   congruence R iff (λx, f1 x ↔ f2 x) := sorry
 
 theorem congr_not [instance] (T : Type) (R : T → T → Prop) (f : T → Prop)
-    (H : congruence R iff f) :
+    [H : congruence R iff f] :
   congruence R iff (λx, ¬ f x) := sorry
 
 theorem subst_iff {T : Type} {R : T → T → Prop} {P : T → Prop} [C : congruence R iff P]
diff --git a/tests/lean/run/univ_bug2.lean b/tests/lean/run/univ_bug2.lean
index d4ce5c812..8b3be7671 100644
--- a/tests/lean/run/univ_bug2.lean
+++ b/tests/lean/run/univ_bug2.lean
@@ -20,7 +20,7 @@ theorem infer_eq {T : Type} (t1 t2 : T) [C : simplifies_to t1 t2] : t1 = t2 :=
 simplifies_to.rec (λx, x) C
 
 theorem simp_app [instance] (S : Type) (T : Type) (f1 f2 : S → T) (s1 s2 : S)
-   (C1 : simplifies_to f1 f2) (C2 : simplifies_to s1 s2) : simplifies_to (f1 s1) (f2 s2) :=
+   [C1 : simplifies_to f1 f2] [C2 : simplifies_to s1 s2] : simplifies_to (f1 s1) (f2 s2) :=
 mk (congr (get_eq C1) (get_eq C2))
 
 theorem test1 (S : Type) (T : Type) (f1 f2 : S → T) (s1 s2 : S) (Hf : f1 = f2) (Hs : s1 = s2) :