diff --git a/main.go b/main.go
index 14ec453..0837fc2 100644
--- a/main.go
+++ b/main.go
@@ -43,5 +43,5 @@ func main() {
 		os.Exit(1)
 	}()
 
-	pmuxlib.Run(ctx, cfg)
+	pmuxlib.Run(ctx, os.Stdout, os.Stderr, cfg)
 }
diff --git a/pmuxlib/pmuxlib.go b/pmuxlib/pmuxlib.go
index b9d6f7e..6d5dfaa 100644
--- a/pmuxlib/pmuxlib.go
+++ b/pmuxlib/pmuxlib.go
@@ -4,7 +4,7 @@ package pmuxlib
 
 import (
 	"context"
-	"os"
+	"io"
 	"sync"
 )
 
@@ -16,12 +16,16 @@ type Config struct {
 // Run runs the given configuration as if this was a real pmux process. It will
 // block until the context is canceled and all child processes have been cleaned
 // up.
-func Run(ctx context.Context, cfg Config) {
+func Run(
+	ctx context.Context,
+	stdout, stderr io.Writer,
+	cfg Config,
+) {
 
-	stdoutLogger := newLogger(os.Stdout, logSepStdout, cfg.TimeFormat)
+	stdoutLogger := newLogger(stdout, logSepStdout, cfg.TimeFormat)
 	defer stdoutLogger.Close()
 
-	stderrLogger := newLogger(os.Stderr, logSepStderr, cfg.TimeFormat)
+	stderrLogger := newLogger(stderr, logSepStderr, cfg.TimeFormat)
 	defer stderrLogger.Close()
 
 	sysLogger := stderrLogger.withSep(logSepSys)