diff --git a/src/components/ui/toggle-group.test.tsx b/src/components/ui/toggle-group.test.tsx
new file mode 100644
index 0000000..af47e6c
--- /dev/null
+++ b/src/components/ui/toggle-group.test.tsx
@@ -0,0 +1,53 @@
+/**
+ * @vitest-environment jsdom
+ *
+ * Arrow-key movement in a ToggleGroup comes from Base UI's composite, which
+ * reads `orientation` off the primitive. Our wrapper takes `orientation` as its
+ * own prop, so it is one destructure away from being spent on the data
+ * attribute and never reaching the composite — which is exactly what happened:
+ * a vertical group answered to Left/Right instead of Up/Down.
+ */
+import { describe, it, expect } from "vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/react";
+import { ToggleGroup, ToggleGroupItem } from "./toggle-group";
+
+function renderGroup(orientation: "horizontal" | "vertical") {
+  render(
+    <ToggleGroup value={["a"]} onValueChange={() => {}} orientation={orientation} aria-label="Test">
+      <ToggleGroupItem value="a">A</ToggleGroupItem>
+      <ToggleGroupItem value="b">B</ToggleGroupItem>
+      <ToggleGroupItem value="c">C</ToggleGroupItem>
+    </ToggleGroup>,
+  );
+  return ["A", "B", "C"].map((n) => screen.getByRole("button", { name: n }));
+}
+
+async function movesFocus(items: HTMLElement[], key: string) {
+  items[0].focus();
+  fireEvent.keyDown(items[0], { key });
+  try {
+    await waitFor(() => expect(document.activeElement).toBe(items[1]), { timeout: 300 });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+describe("ToggleGroup keyboard navigation", () => {
+  it("is a single tab stop, not one per item", () => {
+    const items = renderGroup("horizontal");
+    expect(items.filter((el) => (el as HTMLButtonElement).tabIndex === 0)).toHaveLength(1);
+  });
+
+  it("moves a vertical group with ArrowDown", async () => {
+    expect(await movesFocus(renderGroup("vertical"), "ArrowDown")).toBe(true);
+  });
+
+  it("does not move a vertical group with ArrowRight", async () => {
+    expect(await movesFocus(renderGroup("vertical"), "ArrowRight")).toBe(false);
+  });
+
+  it("moves a horizontal group with ArrowRight", async () => {
+    expect(await movesFocus(renderGroup("horizontal"), "ArrowRight")).toBe(true);
+  });
+});
diff --git a/src/components/ui/toggle-group.tsx b/src/components/ui/toggle-group.tsx
index 4a5b000..e6ba024 100644
--- a/src/components/ui/toggle-group.tsx
+++ b/src/components/ui/toggle-group.tsx
@@ -39,6 +39,10 @@ function ToggleGroup({
       data-variant={variant}
       data-size={size}
       data-spacing={spacing}
+      // Base UI drives arrow-key movement from this, so it has to reach the
+      // primitive and not just the data attribute the styles read. Without it
+      // a vertical group still answered to Left/Right instead of Up/Down.
+      orientation={orientation}
       data-orientation={orientation}
       style={{ "--gap": spacing } as React.CSSProperties}
       className={cn(
diff --git a/vitest.config.ts b/vitest.config.ts
index 0709580..9dfab94 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -7,7 +7,10 @@ export default defineConfig({
   test: {
     globals: true,
     environment: "node",
-    include: ["src/**/*.test.ts", "tests/**/*.test.ts"],
+    // `.tsx` files are component tests; each one declares
+    // `@vitest-environment jsdom` in its own docblock, so the default node
+    // environment still applies to everything else.
+    include: ["src/**/*.test.ts", "src/**/*.test.tsx", "tests/**/*.test.ts"],
     exclude: ["e2e/**", "node_modules/**"],
     globalSetup: ["./tests/global-setup.ts"],
     testTimeout: 30_000,