diff --git a/Makefile b/Makefile
index 6b1c31d66..3e59f27c4 100644
--- a/Makefile
+++ b/Makefile
@@ -20,6 +20,6 @@ clean:
 test:
 	rm -rf _build/_tests
 	jbuilder build --dev test/test.bc test-lwt/test.bc test-bin/calc.bc test-mirage/test.bc
-	#./_build/default/test/test.bc test core -ev 36
+	#./_build/default/test/test.bc test core -ev 12
 	#./_build/default/test-lwt/test.bc test lwt -ev 3
 	jbuilder build @runtest --dev --no-buffer -j 1
diff --git a/capnp-rpc/struct_proxy.ml b/capnp-rpc/struct_proxy.ml
index bb3cd1895..b1c4b6431 100644
--- a/capnp-rpc/struct_proxy.ml
+++ b/capnp-rpc/struct_proxy.ml
@@ -218,7 +218,12 @@ module Make (C : S.CORE_TYPES) = struct
         ~unresolved:(fun _ ->
             match blocker with
             | None -> Some (self :> base_ref)
-            | Some x -> x#blocker
+            | Some x ->
+              match x#blocker with
+              | Some _ as b -> b
+              | None -> 
+                Debug.invariant_broken @@ fun f ->
+                Fmt.pf f "Proxy %t is blocked on non-blocked cap %t!" self#pp x#pp
           )
         ~forwarding:(fun x -> x#blocker)
 
diff --git a/test/test.ml b/test/test.ml
index 3b5a8fabc..11707167f 100644
--- a/test/test.ml
+++ b/test/test.ml
@@ -802,6 +802,46 @@ let test_local_embargo_15 () =
   CS.flush c s;
   CS.check_finished c s
 
+let test_local_embargo_16 () =
+  let client_bs = Services.manual () in
+  let server_bs = Services.manual () in
+  let c, s = CS.create
+    ~client_tags:Test_utils.client_tags ~client_bs
+    ~server_tags:Test_utils.server_tags server_bs
+  in
+  let to_client = S.bootstrap s in
+  let to_server = C.bootstrap c in
+  CS.flush c s;
+  dec_ref @@ call to_client "q1" [];
+  let x2 = call_for_cap to_client "q2" [] in
+  let x3 = call_for_cap x2 "q3" [to_client] in
+  let x4 = call_for_cap x3 "q4" [x3] in
+  C.handle_msg c ~expect:"call:q1";
+  C.handle_msg c ~expect:"finish";
+  C.handle_msg c ~expect:"call:q2";
+  C.handle_msg c ~expect:"call:q3";
+  C.handle_msg c ~expect:"call:q4";
+  let a1 = client_bs#pop0 "q1" in
+  let a2 = client_bs#pop0 "q2" in
+  Core_types.resolve_exn a1 (Capnp_rpc.Exception.v "q1-failed");
+  resolve_ok a2 "reply" [to_server];
+  S.handle_msg s ~expect:"return:(cancelled)";
+  S.handle_msg s ~expect:"call:q3";
+  let to_to_client, a3 = server_bs#pop1 "q3" in
+  Logs.info (fun f -> f "to_to_client = %t, server_bs = %t" to_to_client#pp server_bs#pp);
+  CS.dump c s;
+  S.handle_msg s ~expect:"return:take-from-other";
+  Logs.info (fun f -> f "x3=%t, blocker=%b" x3#pp (x3#blocker <> None));
+  let _ = call x4 "m1" [x3] in  (* x3 gets exported as SenderHosted, despite being a promise *)
+  let _ = call to_to_client "m2" [x3] in
+  CS.flush c s;
+  resolve_ok a3 "reply" [to_to_client];
+  let cr_281, _resolver_280 = client_bs#pop1 "m2" in
+  dec_ref cr_281;
+  CS.dump c s;
+  CS.flush c s;
+  CS.check_finished c s
+
 (* The field must still be useable after the struct is released. *)
 let test_fields () =
   let c, s = CS.create ~client_tags:Test_utils.client_tags ~server_tags:Test_utils.server_tags (Services.echo_service ()) in
@@ -1536,6 +1576,7 @@ let tests = [
   "Local embargo 13", `Quick, test_local_embargo_13;
   "Local embargo 14", `Quick, test_local_embargo_14;
   "Local embargo 15", `Quick, test_local_embargo_15;
+  "Local embargo 16", `Quick, test_local_embargo_16;
   "Shared cap", `Quick, test_share_cap;
   "Fields", `Quick, test_fields;
   "Cancel", `Quick, test_cancel;