diff --git a/include/logging/logger.hpp b/include/logging/logger.hpp
index dc3d72df1..90f0a66c9 100644
--- a/include/logging/logger.hpp
+++ b/include/logging/logger.hpp
@@ -111,4 +111,3 @@ private:
     Log* log;
     std::string name;
 };
-
diff --git a/include/logging/streams/format.hpp b/include/logging/streams/format.hpp
new file mode 100644
index 000000000..94cd1fc33
--- /dev/null
+++ b/include/logging/streams/format.hpp
@@ -0,0 +1,30 @@
+#pragma once
+
+#include <fmt/format.h>
+#include <string>
+
+#include "logging/log.hpp"
+
+// TODO: in c++17 replace with logging::format
+namespace logging
+{
+    namespace format
+    {
+        std::string out = "{} {:<5} [{}] {}\n";
+        std::string err = out;
+
+        // TODO: configurable formats
+    }
+
+    class Formatter
+    {
+    public:
+        static std::string format(const std::string &format,
+                                  const Log::Record &record)
+        {
+            return fmt::format(format, static_cast<std::string>(record.when()),
+                               record.level_str(), record.where(),
+                               record.text());
+        }
+    };
+}
diff --git a/include/logging/streams/stderr.hpp b/include/logging/streams/stderr.hpp
new file mode 100644
index 000000000..a392e666e
--- /dev/null
+++ b/include/logging/streams/stderr.hpp
@@ -0,0 +1,9 @@
+#pragma once
+
+#include "logging/log.hpp"
+
+class Stderr : public Log::Stream
+{
+public:
+    void emit(const Log::Record&) override;
+};
diff --git a/src/logging/streams/stderr.cpp b/src/logging/streams/stderr.cpp
new file mode 100644
index 000000000..5fd354036
--- /dev/null
+++ b/src/logging/streams/stderr.cpp
@@ -0,0 +1,9 @@
+#include "logging/streams/stderr.hpp"
+
+#include <iostream>
+#include "logging/streams/format.hpp"
+
+void Stderr::emit(const Log::Record& record)
+{
+    std::cerr << logging::Formatter::format(logging::format::err, record);
+}
diff --git a/src/logging/streams/stdout.cpp b/src/logging/streams/stdout.cpp
index 17d04806d..999b9122c 100644
--- a/src/logging/streams/stdout.cpp
+++ b/src/logging/streams/stdout.cpp
@@ -1,17 +1,9 @@
 #include "logging/streams/stdout.hpp"
 
 #include <iostream>
-#include <fmt/format.h>
+#include "logging/streams/format.hpp"
 
 void Stdout::emit(const Log::Record& record)
 {
-    auto s = fmt::format("{} {:<5} [{}] {}\n", static_cast<std::string>(
-                         record.when()), record.level_str(), record.where(),
-                         record.text());
-
-    std::cout << s;
-
-    /* fmt::printf("{} {:<5} [{}] {}\n", static_cast<std::string>(record.when()), */
-    /*             record.level_str(), record.where(), record.text()); */
+    std::cout << logging::Formatter::format(logging::format::out, record);
 }
-
diff --git a/tests/unit/concurrent_map.cpp b/tests/unit/concurrent_map.cpp
index b9e008332..6669747f0 100644
--- a/tests/unit/concurrent_map.cpp
+++ b/tests/unit/concurrent_map.cpp
@@ -1,5 +1,7 @@
 #include <iostream>
 
+#include "logging/default.hpp"
+#include "logging/streams/stdout.hpp"
 #include "data_structures/concurrent/concurrent_map.hpp"
 #include "utils/assert.hpp"
 
@@ -8,59 +10,65 @@ using std::endl;
 
 using skiplist_t = ConcurrentMap<int, int>;
 
-void print_skiplist(const skiplist_t::Accessor &skiplist) {
-  cout << "---- skiplist now has: ";
+void print_skiplist(const skiplist_t::Accessor &skiplist)
+{
+    cout << "---- skiplist now has: ";
 
-  for (auto &kv : skiplist)
-    cout << "(" << kv.first << ", " << kv.second << ") ";
+    for (auto &kv : skiplist)
+        cout << "(" << kv.first << ", " << kv.second << ") ";
 
-  cout << "----" << endl;
+    cout << "----" << endl;
 }
 
-int main(void) {
-  skiplist_t skiplist;
-  auto accessor = skiplist.access();
+int main(void)
+{
+    logging::init_async();
+    logging::log->pipe(std::make_unique<Stdout>());
 
-  // insert 10
-  permanent_assert(accessor.insert(1, 10).second == true, "add first element");
+    skiplist_t skiplist;
+    auto accessor = skiplist.access();
 
-  // try insert 10 again (should fail)
-  permanent_assert(accessor.insert(1, 10).second == false,
-                   "add the same element, should fail");
+    // insert 10
+    permanent_assert(accessor.insert(1, 10).second == true,
+                     "add first element");
 
-  // insert 20
-  permanent_assert(accessor.insert(2, 20).second == true,
-                   "insert new unique element");
+    // try insert 10 again (should fail)
+    permanent_assert(accessor.insert(1, 10).second == false,
+                     "add the same element, should fail");
 
-  print_skiplist(accessor);
+    // insert 20
+    permanent_assert(accessor.insert(2, 20).second == true,
+                     "insert new unique element");
 
-  // value at key 3 shouldn't exist
-  permanent_assert((accessor.find(3) == accessor.end()) == true,
-                   "try to find element which doesn't exist");
+    print_skiplist(accessor);
 
-  // value at key 2 should exist
-  permanent_assert((accessor.find(2) != accessor.end()) == true,
-                   "find iterator");
+    // value at key 3 shouldn't exist
+    permanent_assert((accessor.find(3) == accessor.end()) == true,
+                     "try to find element which doesn't exist");
 
-  // at key 2 is 20 (true)
-  permanent_assert(accessor.find(2)->second == 20, "find element");
+    // value at key 2 should exist
+    permanent_assert((accessor.find(2) != accessor.end()) == true,
+                     "find iterator");
 
-  // removed existing (1)
-  permanent_assert(accessor.remove(1) == true, "try to remove element");
+    // at key 2 is 20 (true)
+    permanent_assert(accessor.find(2)->second == 20, "find element");
 
-  // removed non-existing (3)
-  permanent_assert(accessor.remove(3) == false,
-                   "try to remove element which doesn't exist");
+    // removed existing (1)
+    permanent_assert(accessor.remove(1) == true, "try to remove element");
 
-  // insert (1, 10)
-  permanent_assert(accessor.insert(1, 10).second == true,
-                   "insert unique element");
+    // removed non-existing (3)
+    permanent_assert(accessor.remove(3) == false,
+                     "try to remove element which doesn't exist");
 
-  // insert (4, 40)
-  permanent_assert(accessor.insert(4, 40).second == true,
-                   "insert unique element");
+    // insert (1, 10)
+    permanent_assert(accessor.insert(1, 10).second == true,
+                     "insert unique element");
 
-  print_skiplist(accessor);
+    // insert (4, 40)
+    permanent_assert(accessor.insert(4, 40).second == true,
+                     "insert unique element");
 
-  return 0;
+    print_skiplist(accessor);
+
+    return 0;
 }