diff --git a/lib/nodejs/supervisor.ex b/lib/nodejs/supervisor.ex
index a39d9b8..6688296 100644
--- a/lib/nodejs/supervisor.ex
+++ b/lib/nodejs/supervisor.ex
@@ -39,7 +39,7 @@ defmodule NodeJS.Supervisor do
         GenServer.call(pid, {module, args, [binary: binary, timeout: timeout, esm: esm]}, timeout)
       catch
         :exit, {:timeout, _} ->
-          {:error, "Call timed out."}
+          {:error, :timeout}
 
         :exit, error ->
           {:error, {:node_js_worker_exit, error}}
@@ -69,7 +69,7 @@ defmodule NodeJS.Supervisor do
       run_in_transaction(module, args, opts)
     catch
       :exit, {:timeout, _} ->
-        {:error, "Call timed out."}
+        {:error, :timeout}
     end
   end
 
@@ -78,7 +78,8 @@ defmodule NodeJS.Supervisor do
     |> call(args, opts)
     |> case do
       {:ok, result} -> result
-      {:error, message} -> raise NodeJS.Error, message: message
+      {:error, message} when is_binary(message) -> raise NodeJS.Error, message: message
+      {:error, :timeout} -> raise NodeJS.Error, message: "Call timed out."
     end
   end
 
diff --git a/test/nodejs_test.exs b/test/nodejs_test.exs
index 713e5f3..235b9ae 100644
--- a/test/nodejs_test.exs
+++ b/test/nodejs_test.exs
@@ -164,10 +164,10 @@ defmodule NodeJS.Test do
       assert_receive :received_timeout_3, 10
       assert_receive :received_timeout_4, 10
 
-      assert {:error, "Call timed out."} = Task.await(task1)
-      assert {:error, "Call timed out."} = Task.await(task2)
-      assert {:error, "Call timed out."} = Task.await(task3)
-      assert {:error, "Call timed out."} = Task.await(task4)
+      assert {:error, :timeout} = Task.await(task1)
+      assert {:error, :timeout} = Task.await(task2)
+      assert {:error, :timeout} = Task.await(task3)
+      assert {:error, :timeout} = Task.await(task4)
 
       # We should still get an answer here, before the timeout
       assert {:ok, 1115} = NodeJS.call("slow-async-echo", [1115, 1])
@@ -176,7 +176,7 @@ defmodule NodeJS.Test do
 
   describe "overriding call timeout" do
     test "works, and you can tell because the slow function will time out" do
-      assert {:error, "Call timed out."} = NodeJS.call("slow-async-echo", [1111], timeout: 0)
+      assert {:error, :timeout} = NodeJS.call("slow-async-echo", [1111], timeout: 0)
       assert_raise NodeJS.Error, fn -> NodeJS.call!("slow-async-echo", [1111], timeout: 0) end
       assert {:ok, 1111} = NodeJS.call("slow-async-echo", [1111])
     end
@@ -190,9 +190,9 @@ defmodule NodeJS.Test do
 
   describe "Implementation details shouldn't leak:" do
     test "Timeouts do not send stray messages to calling process" do
-      assert {:error, "Call timed out."} = NodeJS.call("slow-async-echo", [1111], timeout: 0)
+      assert {:error, :timeout} = NodeJS.call("slow-async-echo", [1111], timeout: 0)
 
-      refute_receive {_ref, {:error, "Call timed out."}}, 50
+      refute_receive {_ref, {:error, :timeout}}, 50
     end
 
     test "Crashes do not bring down the calling process" do