diff --git a/cmd/ghostty-switch/main_test.go b/cmd/ghostty-switch/main_test.go
index 817dc22..a41ccc0 100644
--- a/cmd/ghostty-switch/main_test.go
+++ b/cmd/ghostty-switch/main_test.go
@@ -179,6 +179,32 @@ func TestCLIProfileApply(t *testing.T) {
 	}
 }
 
+func TestCLIProfileApplyClearsListValuedKeys(t *testing.T) {
+	bin := buildBinary(t)
+	dir := t.TempDir()
+	overridePath := filepath.Join(dir, "overrides")
+	configPath := writeTestConfig(t, dir, overridePath)
+
+	cmd := exec.Command(bin, "--config", configPath, "profile", "dark")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("profile dark: %v\n%s", err, out)
+	}
+
+	data, err := os.ReadFile(overridePath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// The dark profile sets font-family, which Ghostty treats as list-valued.
+	// The override file must emit a clearing line before the value line so the
+	// override replaces — rather than appends to — the main config's font-family.
+	wantPair := "font-family =\nfont-family = JetBrains Mono\n"
+	if !strings.Contains(string(data), wantPair) {
+		t.Errorf("override file missing clearing+value pair %q, got:\n%s", wantPair, data)
+	}
+}
+
 func TestCLIConfigFlagWithoutValue(t *testing.T) {
 	bin := buildBinary(t)
 	cmd := exec.Command(bin, "--config")
diff --git a/internal/overrides/overrides.go b/internal/overrides/overrides.go
index 9411caa..cc69eb3 100644
--- a/internal/overrides/overrides.go
+++ b/internal/overrides/overrides.go
@@ -12,6 +12,19 @@ import (
 
 const header = "# Managed by ghostty-switch — do not edit manually"
 
+// listValuedKeys are Ghostty config directives that accumulate across
+// occurrences (each line appends to a list) rather than scalar last-write-wins.
+// Each is preceded in the override file by a clearing line ("key =") so the
+// override replaces — rather than appends to — values from the main config
+// that loaded earlier. See issue #20.
+var listValuedKeys = map[string]struct{}{
+	"font-family":             {},
+	"font-family-bold":        {},
+	"font-family-italic":      {},
+	"font-family-bold-italic": {},
+	"keybind":                 {},
+}
+
 // Read parses the override file into a key-value map. Returns an empty map
 // if the file does not exist.
 func Read(path string) (map[string]string, error) {
@@ -59,6 +72,9 @@ func Write(path string, settings map[string]string) error {
 
 	keys := sortedKeys(settings)
 	for _, k := range keys {
+		if _, isList := listValuedKeys[k]; isList {
+			fmt.Fprintf(&b, "%s =\n", k)
+		}
 		fmt.Fprintf(&b, "%s = %s\n", k, settings[k])
 	}
 
diff --git a/internal/overrides/overrides_test.go b/internal/overrides/overrides_test.go
index fed294c..616c59e 100644
--- a/internal/overrides/overrides_test.go
+++ b/internal/overrides/overrides_test.go
@@ -119,6 +119,96 @@ func TestReadSkipsCommentsAndBlanks(t *testing.T) {
 	}
 }
 
+func TestWriteEmitsClearingLineForListValuedKeys(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overrides")
+
+	settings := map[string]string{
+		"font-family": "MartianMono Nerd Font",
+		"font-size":   "14",
+		"theme":       "Nord",
+	}
+
+	if err := Write(path, settings); err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+
+	data, _ := os.ReadFile(path)
+	content := string(data)
+
+	// Clearing line must precede the value line, consecutive, for list-valued keys.
+	wantPair := "font-family =\nfont-family = MartianMono Nerd Font\n"
+	if !strings.Contains(content, wantPair) {
+		t.Errorf("expected output to contain clearing+value pair %q, got:\n%s", wantPair, content)
+	}
+
+	// Scalar keys must not get a clearing line.
+	for _, scalar := range []string{"font-size", "theme"} {
+		bare := scalar + " =\n"
+		if strings.Contains(content, bare) {
+			t.Errorf("scalar key %q must not have a clearing line; got:\n%s", scalar, content)
+		}
+	}
+}
+
+func TestWriteEmitsClearingLineForEachListValuedKey(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overrides")
+
+	settings := map[string]string{
+		"font-family":             "Mono",
+		"font-family-bold":        "Mono Bold",
+		"font-family-italic":      "Mono Italic",
+		"font-family-bold-italic": "Mono Bold Italic",
+		"keybind":                 "ctrl+a=copy_to_clipboard",
+	}
+
+	if err := Write(path, settings); err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+
+	content := func() string {
+		data, _ := os.ReadFile(path)
+		return string(data)
+	}()
+
+	for k, v := range settings {
+		want := k + " =\n" + k + " = " + v + "\n"
+		if !strings.Contains(content, want) {
+			t.Errorf("expected clearing+value pair for %q (%q), got:\n%s", k, want, content)
+		}
+	}
+}
+
+func TestReadWriteRoundTripPreservesListValuedKeys(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overrides")
+
+	original := map[string]string{
+		"font-family": "MartianMono Nerd Font",
+		"keybind":     "ctrl+a=copy_to_clipboard",
+		"theme":       "Nord",
+	}
+
+	if err := Write(path, original); err != nil {
+		t.Fatalf("Write: %v", err)
+	}
+
+	got, err := Read(path)
+	if err != nil {
+		t.Fatalf("Read: %v", err)
+	}
+
+	if len(got) != len(original) {
+		t.Errorf("expected %d entries, got %d: %v", len(original), len(got), got)
+	}
+	for k, v := range original {
+		if got[k] != v {
+			t.Errorf("key %q = %q, want %q", k, got[k], v)
+		}
+	}
+}
+
 func TestMerge(t *testing.T) {
 	existing := map[string]string{
 		"theme":     "Nord",