diff --git a/README.md b/README.md
index 5dec016..19b5170 100644
--- a/README.md
+++ b/README.md
@@ -33,7 +33,7 @@ creating, grouping, pausing, running, and monitoring scheduled shell commands.
 - Desktop notifications on job failure.
 - Windows tray icon: left-click to show the window, right-click for the menu.
 - Autostart on login (Windows shortcut; Linux XDG desktop entry).
-- Detailed or compact job list, and a default or branded theme; both are remembered.
+- Detailed or compact job list, and a system or branded theme; both are remembered.
 
 ## Platforms
 
@@ -83,7 +83,7 @@ That is the file GoSentry writes on first run. `default_timeout_seconds` is the
 run timeout applied to jobs that do not set their own; `0` means no timeout, and
 it is written out even though it is zero, because a missing value and a
 deliberate "no timeout" have to stay distinguishable in a hand-edited file.
-`theme` is `default` or `gosentry` (the branded teal/amber look), and
+`theme` is `system` or `gosentry` (the branded teal/amber look), and
 `job_list_view` is `detailed` or `compact` — both are remembered from the
 choices made in the app. Keys left at their off value (`start_on_login`,
 `paused`) are omitted until they are turned on.
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 6ecfe09..76dadf5 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -40,8 +40,10 @@ dragged.**
 
 - **The branded GoSentry theme is now the default.** Fresh installs, the
   **Defaults** button, and configs that omit `theme` all open in the teal/amber
-  look; users who prefer Fyne's built-in theme can still pick **Default** in
+  look; users who prefer Fyne's built-in theme can still pick **System** in
   Settings.
+- The Fyne built-in theme option is labelled **System** (stored as `"system"`);
+  configs that still say `"default"` are read as System and rewritten on save.
 - The **Save / Cancel / Restore defaults** row sits 4 px from the left edge, as
   its layout always intended, rather than 8.
 - The caption column is as wide as the widest caption instead of a fixed width,
diff --git a/docs/TESTS.md b/docs/TESTS.md
index 8995df1..56159e1 100644
--- a/docs/TESTS.md
+++ b/docs/TESTS.md
@@ -237,6 +237,7 @@ Tests JSON round-tripping, default generation, and backward compatibility.
 | `TestLoadOrCreateConfigCreatesDefaultsOnFirstRun` | Verifies that a missing config file is created with sane defaults and a sample job. |
 | `TestLoadOrCreateConfigKeepsZeroTimeoutOnReload` | Verifies that `default_timeout_seconds: 0` survives a reload rather than being normalized away — 0 is a value, not a missing field. |
 | `TestLoadOrCreateConfigMigratesJobsDir` | Verifies that a pre-0.15 `jobs_dir` becomes `jobs_file` pointing at the same `jobs.json`, and that the retired key is not written back. |
+| `TestLoadOrCreateConfigMigratesLegacyThemeDefault` | Verifies that a config storing the retired `"default"` theme value is normalized to `system` on load. |
 | `TestLoadJobsFileReportsMissingWithoutCreating` | Verifies that `LoadJobsFile` reports a missing file as not-found without creating or seeding it, and normalizes the jobs it does load. |
 | `TestApplyConfigPathsDerivesJobsDir` | Verifies that the configured jobs file resolves against the program folder and that `Paths.JobsDir` is derived from it. |
 | `TestJobTimeoutRoundTripsThreeStates` | Verifies the on-disk encoding that keeps "inherit" and "no timeout" distinguishable: `nil` is omitted entirely, an explicit `0` is written and read back as set. |
@@ -514,8 +515,8 @@ Tests the branded theme and the stored theme choice.
 |------|---------|
 | `TestGoSentryThemeBrandColors` | Verifies the brand colors land on the semantically correct `ColorName`s in both the light and dark variants. |
 | `TestGoSentryThemeDelegatesUnbrandedColors` | Verifies unbranded color names fall through to the base theme rather than rendering transparent. |
-| `TestThemeForChoice` | Verifies the GoSentry choice and the empty legacy value yield the branded primary; only the explicit default choice yields Fyne's built-in theme. |
-| `TestThemeLabelRoundTrip` | Verifies the dropdown labels round-trip and that the empty value maps to the Default label rather than a blank option. |
+| `TestThemeForChoice` | Verifies the GoSentry choice and the empty legacy value yield the branded primary; only the explicit system choice yields Fyne's built-in theme. |
+| `TestThemeLabelRoundTrip` | Verifies the dropdown labels round-trip and that the empty value maps to the GoSentry label rather than a blank option. |
 
 ---
 
diff --git a/src/app/operations.go b/src/app/operations.go
index a6cb9eb..5137075 100644
--- a/src/app/operations.go
+++ b/src/app/operations.go
@@ -483,8 +483,8 @@ func validateConfig(config domain.Config) error {
 	}
 	// Empty Theme is accepted and normalized to the branded theme on load, so
 	// older configs (and hand-built ones) stay valid without an explicit theme.
-	if config.Theme != "" && config.Theme != domain.ThemeDefault && config.Theme != domain.ThemeGoSentry {
-		return errors.New("theme must be 'default' or 'gosentry'")
+	if config.Theme != "" && config.Theme != domain.ThemeSystem && config.Theme != domain.ThemeGoSentry {
+		return errors.New("theme must be 'system' or 'gosentry'")
 	}
 	return nil
 }
diff --git a/src/domain/config.go b/src/domain/config.go
index bfb1643..a83175b 100644
--- a/src/domain/config.go
+++ b/src/domain/config.go
@@ -21,8 +21,8 @@ const (
 type Theme string
 
 const (
-	// ThemeDefault keeps Fyne's built-in theme — the original look.
-	ThemeDefault Theme = "default"
+	// ThemeSystem keeps Fyne's built-in theme, following the platform look.
+	ThemeSystem Theme = "system"
 	// ThemeGoSentry applies the branded teal/amber theme derived from the logo
 	// and app icon.
 	ThemeGoSentry Theme = "gosentry"
diff --git a/src/storage/store.go b/src/storage/store.go
index 3c87190..e35c685 100644
--- a/src/storage/store.go
+++ b/src/storage/store.go
@@ -120,6 +120,9 @@ func loadOrCreateConfig(paths Paths) (domain.Config, error) {
 	if config.Theme == "" {
 		config.Theme = domain.ThemeGoSentry
 	}
+	if config.Theme == "default" {
+		config.Theme = domain.ThemeSystem
+	}
 	return config, nil
 }
 
diff --git a/src/storage/store_test.go b/src/storage/store_test.go
index 905f77f..a07b1f4 100644
--- a/src/storage/store_test.go
+++ b/src/storage/store_test.go
@@ -183,6 +183,34 @@ func TestLoadOrCreateConfigCreatesDefaultsOnFirstRun(t *testing.T) {
 	}
 }
 
+// TestLoadOrCreateConfigMigratesLegacyThemeDefault covers a gosentry.json that
+// still stores the retired "default" theme value: load normalizes it to system.
+func TestLoadOrCreateConfigMigratesLegacyThemeDefault(t *testing.T) {
+	dir := t.TempDir()
+	paths := Paths{
+		AppDir:     dir,
+		ConfigPath: filepath.Join(dir, ConfigFileName),
+	}
+	legacy := map[string]any{
+		"jobs_file":        "jobs.json",
+		"logs_dir":         "logs",
+		"max_log_files":    100,
+		"max_log_age_days": 30,
+		"theme":            "default",
+	}
+	if err := writeJSON(paths.ConfigPath, legacy); err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := loadOrCreateConfig(paths)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Theme != domain.ThemeSystem {
+		t.Errorf("migrated Theme = %q, want %q", got.Theme, domain.ThemeSystem)
+	}
+}
+
 // TestLoadOrCreateConfigKeepsZeroTimeoutOnReload guards the "0 = no timeout"
 // setting against being normalized away when an existing gosentry.json is read
 // back. Loading must not treat 0 as a missing value.
diff --git a/src/ui/settings_view.go b/src/ui/settings_view.go
index f34cf86..73afb4f 100644
--- a/src/ui/settings_view.go
+++ b/src/ui/settings_view.go
@@ -61,7 +61,7 @@ func settingsView(w fyne.Window, svc *app.Service) fyne.CanvasObject {
 	notifications := widget.NewCheck("Show desktop notifications for failed jobs", nil)
 	notifications.SetChecked(store.Config.NotifyOnFailure)
 	notifications.OnChanged = func(bool) { updateSaveState() }
-	themeSelect := widget.NewSelect([]string{themeLabelDefault, themeLabelGoSentry}, nil)
+	themeSelect := widget.NewSelect([]string{themeLabelSystem, themeLabelGoSentry}, nil)
 	themeSelect.SetSelected(themeLabel(store.Config.Theme))
 	// Preview the theme the moment it is picked so the choice is visible before
 	// saving; Save persists it. Reverting the selection reverts the preview, and
@@ -256,15 +256,15 @@ func settingsView(w fyne.Window, svc *app.Service) fyne.CanvasObject {
 
 // Theme dropdown labels. These are the human-facing captions; themeLabel and
 // themeFromLabel translate between them and the stored domain.Theme values so the
-// select never leaks the on-disk "default"/"gosentry" strings to the user.
+// select never leaks the on-disk "system"/"gosentry" strings to the user.
 const (
-	themeLabelDefault  = "Default"
+	themeLabelSystem   = "System"
 	themeLabelGoSentry = "GoSentry"
 )
 
 func themeLabel(choice domain.Theme) string {
-	if choice == domain.ThemeDefault {
-		return themeLabelDefault
+	if choice == domain.ThemeSystem {
+		return themeLabelSystem
 	}
 	return themeLabelGoSentry
 }
@@ -273,5 +273,5 @@ func themeFromLabel(label string) domain.Theme {
 	if label == themeLabelGoSentry {
 		return domain.ThemeGoSentry
 	}
-	return domain.ThemeDefault
+	return domain.ThemeSystem
 }
diff --git a/src/ui/theme.go b/src/ui/theme.go
index 2e382ff..192c340 100644
--- a/src/ui/theme.go
+++ b/src/ui/theme.go
@@ -104,10 +104,10 @@ func (t gosentryTheme) Icon(name fyne.ThemeIconName) fyne.Resource { return t.ba
 func (t gosentryTheme) Size(name fyne.ThemeSizeName) float32 { return t.base.Size(name) }
 
 // themeFor maps a stored Theme choice to a concrete fyne.Theme. Only the
-// explicit default choice keeps Fyne's built-in theme; everything else
+// explicit system choice keeps Fyne's built-in theme; everything else
 // (including the empty/legacy value) uses the branded GoSentry theme.
 func themeFor(choice domain.Theme) fyne.Theme {
-	if choice == domain.ThemeDefault {
+	if choice == domain.ThemeSystem {
 		return theme.DefaultTheme()
 	}
 	return newGoSentryTheme()
diff --git a/src/ui/theme_test.go b/src/ui/theme_test.go
index 723d58a..e28dc06 100644
--- a/src/ui/theme_test.go
+++ b/src/ui/theme_test.go
@@ -55,7 +55,7 @@ func TestGoSentryThemeDelegatesUnbrandedColors(t *testing.T) {
 }
 
 // themeFor maps the stored choice to the right theme: the GoSentry choice and the
-// empty legacy value yield the branded teal primary; only the explicit default
+// empty legacy value yield the branded teal primary; only the explicit system
 // choice yields Fyne's built-in theme.
 func TestThemeForChoice(t *testing.T) {
 	for _, choice := range []domain.Theme{domain.ThemeGoSentry, ""} {
@@ -64,9 +64,9 @@ func TestThemeForChoice(t *testing.T) {
 			t.Errorf("themeFor(%q) primary = %v, want brand teal %v", choice, got, brandTeal)
 		}
 	}
-	def := themeFor(domain.ThemeDefault)
-	if got := def.Color(theme.ColorNamePrimary, theme.VariantLight); got == brandTeal {
-		t.Errorf("themeFor(default) should not use the brand teal primary")
+	sys := themeFor(domain.ThemeSystem)
+	if got := sys.Color(theme.ColorNamePrimary, theme.VariantLight); got == brandTeal {
+		t.Errorf("themeFor(system) should not use the brand teal primary")
 	}
 }
 
@@ -76,8 +76,8 @@ func TestThemeLabelRoundTrip(t *testing.T) {
 	if got := themeFromLabel(themeLabel(domain.ThemeGoSentry)); got != domain.ThemeGoSentry {
 		t.Errorf("round-trip gosentry = %q", got)
 	}
-	if got := themeFromLabel(themeLabel(domain.ThemeDefault)); got != domain.ThemeDefault {
-		t.Errorf("round-trip default = %q", got)
+	if got := themeFromLabel(themeLabel(domain.ThemeSystem)); got != domain.ThemeSystem {
+		t.Errorf("round-trip system = %q", got)
 	}
 	if got := themeLabel(""); got != themeLabelGoSentry {
 		t.Errorf("empty theme label = %q, want %q", got, themeLabelGoSentry)