diff --git a/test/tests.cpp b/test/tests.cpp
index 3fecd27..cfa94af 100644
--- a/test/tests.cpp
+++ b/test/tests.cpp
@@ -117,7 +117,7 @@ extern "C" auto runtestcase(const char *name) -> int {
   env_t log_env{};
   auto trace = [&](const buffer &buf) {
     const lock_guard<mutex> lock(trace_m);
-    cout << buf.to_json() << '\n';
+    cerr << buf.to_json() << '\n';
   };
   log_env.on_trace(trace);
   env.on_trace(trace);