diff --git a/canvas/src/components/__tests__/Tooltip.test.tsx b/canvas/src/components/__tests__/Tooltip.test.tsx
index e5b07f7e..ec82240b 100644
--- a/canvas/src/components/__tests__/Tooltip.test.tsx
+++ b/canvas/src/components/__tests__/Tooltip.test.tsx
@@ -269,4 +269,19 @@ describe("Tooltip — aria-describedby", () => {
     // The describedby id matches the tooltip id in the portal
     expect(document.getElementById(describedBy!)).toBeTruthy();
   });
+
+  // WCAG 1.4.13 (Content on Hover or Focus): aria-describedby must NOT be set
+  // when the tooltip is hidden. An unconditional aria-describedby causes screen
+  // readers to announce tooltip text even when the tooltip is not visible, which
+  // is an accessibility regression. The fix makes it conditional on `show`.
+  it("does NOT set aria-describedby when tooltip is hidden (WCAG 1.4.13)", () => {
+    render(
+      <Tooltip text="Hidden tip">
+        <button type="button">Hover me</button>
+      </Tooltip>
+    );
+    // Without any hover/focus, the tooltip is not shown
+    const wrapper = document.body.querySelector('[aria-describedby]');
+    expect(wrapper).toBeNull();
+  });
 });