diff --git a/go.mod b/go.mod
index c3bb887..798f8e9 100644
--- a/go.mod
+++ b/go.mod
@@ -6,6 +6,7 @@ require (
 	github.com/docker/docker v28.0.1+incompatible
 	github.com/docker/go-connections v0.5.0
 	github.com/gdamore/tcell/v2 v2.8.1
+	github.com/google/go-cmp v0.7.0
 	github.com/opencontainers/image-spec v1.1.1
 	github.com/rivo/tview v0.0.0-20241227133733-17b7edb88c57
 	github.com/stretchr/testify v1.10.0
diff --git a/internal/config/config.go b/internal/config/config.go
index bc3247b..c1a3daf 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -1,5 +1,7 @@
 package config
 
+import "cmp"
+
 // Destination holds the configuration for a destination.
 type Destination struct {
 	Name string `yaml:"name"`
@@ -10,6 +12,14 @@ type Destination struct {
 type LogFile struct {
 	Enabled bool   `yaml:"enabled"`
 	Path    string `yaml:"path,omitempty"`
+
+	defaultPath string
+}
+
+// GetPath returns the path to the log file. If the path is not set, it
+// returns the default log path.
+func (l LogFile) GetPath() string {
+	return cmp.Or(l.Path, l.defaultPath)
 }
 
 // RTMPSource holds the configuration for the RTMP source.
diff --git a/internal/config/service.go b/internal/config/service.go
index 6b7fd1c..3169759 100644
--- a/internal/config/service.go
+++ b/internal/config/service.go
@@ -47,6 +47,7 @@ func NewService(configDirFunc ConfigDirFunc, chanSize int) (*Service, error) {
 		return nil, fmt.Errorf("app config dir: %w", err)
 	}
 
+	// TODO: inject StateDirFunc
 	appStateDir, err := createAppStateDir()
 	if err != nil {
 		return nil, fmt.Errorf("app state dir: %w", err)
@@ -58,7 +59,7 @@ func NewService(configDirFunc ConfigDirFunc, chanSize int) (*Service, error) {
 		configC:      make(chan Config, chanSize),
 	}
 
-	svc.setDefaults(&svc.current)
+	svc.populateConfigOnBuild(&svc.current)
 
 	return svc, nil
 }
@@ -127,6 +128,7 @@ func (s *Service) readConfig() (cfg Config, _ error) {
 		return cfg, fmt.Errorf("unmarshal: %w", err)
 	}
 
+	s.populateConfigOnRead(&cfg)
 	if err = validate(cfg); err != nil {
 		return cfg, err
 	}
@@ -138,7 +140,7 @@ func (s *Service) readConfig() (cfg Config, _ error) {
 
 func (s *Service) writeDefaultConfig() (Config, error) {
 	var cfg Config
-	s.setDefaults(&cfg)
+	s.populateConfigOnBuild(&cfg)
 
 	cfgBytes, err := marshalConfig(cfg)
 	if err != nil {
@@ -175,10 +177,24 @@ func (s *Service) writeConfig(cfgBytes []byte) error {
 	return nil
 }
 
-// setDefaults is called to set default values for a new, empty configuration.
-func (s *Service) setDefaults(cfg *Config) {
+// populateConfigOnBuild is called to set default values for a new, empty
+// configuration.
+//
+// This function may set exported fields to arbitrary values.
+func (s *Service) populateConfigOnBuild(cfg *Config) {
 	cfg.Sources.RTMP.Enabled = true
 	cfg.Sources.RTMP.StreamKey = "live"
+
+	s.populateConfigOnRead(cfg)
+}
+
+// populateConfigOnRead is called to set default values for a configuration
+// read from an existing file.
+//
+// This function should not update any exported values, which would be a
+// confusing experience for the user.
+func (s *Service) populateConfigOnRead(cfg *Config) {
+	cfg.LogFile.defaultPath = filepath.Join(s.appStateDir, "octoplex.log")
 }
 
 // TODO: validate URL format
diff --git a/internal/config/service_test.go b/internal/config/service_test.go
index c68daf2..e719c69 100644
--- a/internal/config/service_test.go
+++ b/internal/config/service_test.go
@@ -4,10 +4,13 @@ import (
 	_ "embed"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 
 	"git.netflux.io/rob/octoplex/internal/config"
 	"git.netflux.io/rob/octoplex/internal/shortid"
+	gocmp "github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"gopkg.in/yaml.v3"
@@ -19,6 +22,9 @@ var configComplete []byte
 //go:embed testdata/logfile.yml
 var configLogfile []byte
 
+//go:embed testdata/no-logfile.yml
+var configNoLogfile []byte
+
 //go:embed testdata/invalid-destination-url.yml
 var configInvalidDestinationURL []byte
 
@@ -49,7 +55,8 @@ func TestConfigServiceCreateConfig(t *testing.T) {
 
 	cfg, err := service.ReadOrCreateConfig()
 	require.NoError(t, err)
-	require.Empty(t, cfg.LogFile, "expected no log file")
+	require.False(t, cfg.LogFile.Enabled, "expected logging to be disabled")
+	require.Empty(t, cfg.LogFile.Path, "expected no log file")
 
 	p := filepath.Join(systemConfigDir, "octoplex", "config.yaml")
 	cfgBytes, err := os.ReadFile(p)
@@ -71,26 +78,31 @@ func TestConfigServiceReadConfig(t *testing.T) {
 			name:        "complete",
 			configBytes: configComplete,
 			want: func(t *testing.T, cfg config.Config) {
-				require.Equal(
+				require.Empty(
 					t,
-					config.Config{
-						LogFile: config.LogFile{
-							Enabled: true,
-							Path:    "test.log",
-						},
-						Sources: config.Sources{
-							RTMP: config.RTMPSource{
-								Enabled:   true,
-								StreamKey: "s3cr3t",
+					gocmp.Diff(
+						config.Config{
+							LogFile: config.LogFile{
+								Enabled: true,
+								Path:    "test.log",
+							},
+							Sources: config.Sources{
+								RTMP: config.RTMPSource{
+									Enabled:   true,
+									StreamKey: "s3cr3t",
+								},
+							},
+							Destinations: []config.Destination{
+								{
+									Name: "my stream",
+									URL:  "rtmp://rtmp.example.com:1935/live",
+								},
 							},
 						},
-						Destinations: []config.Destination{
-							{
-								Name: "my stream",
-								URL:  "rtmp://rtmp.example.com:1935/live",
-							},
-						},
-					}, cfg)
+						cfg,
+						cmpopts.IgnoreUnexported(config.LogFile{}),
+					),
+				)
 			},
 		},
 		{
@@ -100,6 +112,13 @@ func TestConfigServiceReadConfig(t *testing.T) {
 				assert.Equal(t, "/tmp/octoplex.log", cfg.LogFile.Path)
 			},
 		},
+		{
+			name:        "logging enabled, no logfile",
+			configBytes: configNoLogfile,
+			want: func(t *testing.T, cfg config.Config) {
+				assert.True(t, strings.HasSuffix(cfg.LogFile.GetPath(), "/octoplex/octoplex.log"), "expected %q to end with /tmp/octoplex.log", cfg.LogFile.GetPath())
+			},
+		},
 		{
 			name:        "invalid destination URL",
 			configBytes: configInvalidDestinationURL,
diff --git a/internal/config/testdata/no-logfile.yml b/internal/config/testdata/no-logfile.yml
new file mode 100644
index 0000000..1825093
--- /dev/null
+++ b/internal/config/testdata/no-logfile.yml
@@ -0,0 +1,5 @@
+---
+logfile:
+  enabled: true
+destinations:
+- url: rtmp://rtmp.example.com:1935/live
diff --git a/main.go b/main.go
index c242e17..c77860c 100644
--- a/main.go
+++ b/main.go
@@ -162,7 +162,7 @@ func buildLogger(cfg config.LogFile) (*slog.Logger, error) {
 		return slog.New(slog.DiscardHandler), nil
 	}
 
-	fptr, err := os.OpenFile(cfg.Path, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
+	fptr, err := os.OpenFile(cfg.GetPath(), os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
 	if err != nil {
 		return nil, fmt.Errorf("error opening log file: %w", err)
 	}