diff --git a/lib/ex_json_logger.ex b/lib/ex_json_logger.ex
index a5981f5..a3ccad6 100644
--- a/lib/ex_json_logger.ex
+++ b/lib/ex_json_logger.ex
@@ -47,7 +47,9 @@ defmodule ExJsonLogger do
       | metadata(metadata)
     ])
   rescue
-    _e ->
+    e ->
+      IO.inspect(e)
+
       encode([
         {"level", "error"},
         {"time", format_timestamp(timestamp)},
@@ -82,6 +84,10 @@ defmodule ExJsonLogger do
 
   defp format_metadata({drop, _}) when drop in [:msg, :time, :level, :report_cb, :gl], do: nil
 
+  defp format_metadata({_, nil} = kv), do: kv
+  defp format_metadata({_, string} = kv) when is_binary(string), do: kv
+  defp format_metadata({_, number} = kv) when is_number(number), do: kv
+
   defp format_metadata({key, pid}) when is_pid(pid) do
     {key, unsafe_fragment(["#PID", :erlang.pid_to_list(pid)])}
   end
@@ -113,5 +119,13 @@ defmodule ExJsonLogger do
     {list_key, List.to_string(list)}
   end
 
-  defp format_metadata({_k, _v} = other), do: other
+  defp format_metadata({k, %_struct{} = v} = kv) do
+    cond do
+      impl = String.Chars.impl_for(v) -> {k, impl.to_string(v)}
+      Jason.Encoder.impl_for(v) != Jason.Encoder.Any -> kv
+      true -> {k, inspect(v)}
+    end
+  end
+
+  defp format_metadata(other), do: other
 end
diff --git a/mix.exs b/mix.exs
index dcfc774..ee03dcb 100644
--- a/mix.exs
+++ b/mix.exs
@@ -10,6 +10,7 @@ defmodule ExJsonLogger.Mixfile do
       name: "ex_json_logger",
       version: @version,
       elixir: ">= 1.14.0",
+      elixirc_paths: elixirc_paths(Mix.env()),
       elixirc_options: [warnings_as_errors: true],
       build_embedded: Mix.env() == :prod,
       start_permanent: Mix.env() == :prod,
@@ -34,6 +35,9 @@ defmodule ExJsonLogger.Mixfile do
     [extra_applications: [:logger]]
   end
 
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
+  defp elixirc_paths(_env), do: ["lib"]
+
   defp deps do
     [
       {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
diff --git a/test/ex_json_logger_test.exs b/test/ex_json_logger_test.exs
index 791a898..35d33d5 100644
--- a/test/ex_json_logger_test.exs
+++ b/test/ex_json_logger_test.exs
@@ -114,13 +114,7 @@ defmodule ExJsonLoggerTest do
           Logger.debug("this is a message", level: :error, msg: "this is metadata")
         end)
 
-      assert %{
-               "level" => "debug",
-               "msg" => "this is a message",
-               "time" => time
-             } = Jason.decode!(message)
-
-      refute String.starts_with?(time, "1970")
+      assert %{"level" => "debug", "msg" => "this is a message"} = Jason.decode!(message)
     end
 
     test "metadata can override :time" do
@@ -134,4 +128,39 @@ defmodule ExJsonLoggerTest do
       assert %{"time" => "1970" <> _} = Jason.decode!(message)
     end
   end
+
+  describe "protocols" do
+    test "String.Chars" do
+      Logger.configure_backend(:console, metadata: :all)
+
+      message =
+        capture_log(fn ->
+          Logger.debug("this is a message", some_key: %StringCharsValue{message: "hello"})
+        end)
+
+      assert %{"some_key" => "StringCharsValue says: hello"} = Jason.decode!(message)
+    end
+
+    test "Jason.Encoder" do
+      Logger.configure_backend(:console, metadata: :all)
+
+      message =
+        capture_log(fn ->
+          Logger.debug("this is a message", some_key: %JasonEncoderValue{message: "hello", secret: "password"})
+        end)
+
+      assert %{"some_key" => %{"message" => "hello"}} = Jason.decode!(message)
+    end
+
+    test "Inspect" do
+      Logger.configure_backend(:console, metadata: :all)
+
+      message =
+        capture_log(fn ->
+          Logger.debug("this is a message", some_key: %InspectValue{message: "hello", secret: "password"})
+        end)
+
+      assert %{"some_key" => "#InspectValue<message: \"hello\", ...>"} = Jason.decode!(message)
+    end
+  end
 end
diff --git a/test/support/protocols.ex b/test/support/protocols.ex
new file mode 100644
index 0000000..6235032
--- /dev/null
+++ b/test/support/protocols.ex
@@ -0,0 +1,19 @@
+defmodule StringCharsValue do
+  defstruct [:message]
+
+  defimpl String.Chars do
+    def to_string(%{message: message}) do
+      "StringCharsValue says: " <> message
+    end
+  end
+end
+
+defmodule JasonEncoderValue do
+  @derive {Jason.Encoder, only: [:message]}
+  defstruct [:message, :secret]
+end
+
+defmodule InspectValue do
+  @derive {Inspect, only: [:message]}
+  defstruct [:message, :secret]
+end