diff --git a/test/csys_test.exs b/test/csys_test.exs
index 6ab9c21..b7cc7e9 100644
--- a/test/csys_test.exs
+++ b/test/csys_test.exs
@@ -28,7 +28,7 @@ defmodule Scopes.CSysTest do
       Environ.forward_value(env, [:csys, :s01, {1, 1}], 3)
       assert receive_data().value in [2, 3]
       assert receive_data().value in [2, 3]
-      refute_received msg, "unhandled message(s): #{inspect(msg)}"
+      refute_receive msg, 30, "unhandled message(s): #{inspect(msg)}"
     end
 
     test "recursive-1" do
@@ -38,8 +38,7 @@ defmodule Scopes.CSysTest do
       assert receive_data().value == 42
       Environ.forward_value(env, [:csys, :s01, {1, 1}], 47)
       assert receive_data().value == 5
-      Process.sleep(30)
-      refute_received msg, "unhandled message(s): #{inspect(msg)}"
+      refute_receive msg, 30, "unhandled message(s): #{inspect(msg)}"
     end
   end
 end