diff --git a/web/src/components/ui/select.tsx b/web/src/components/ui/select.tsx
index 6f728a22..41b04f71 100644
--- a/web/src/components/ui/select.tsx
+++ b/web/src/components/ui/select.tsx
@@ -71,6 +71,7 @@ function SelectContent({
         alignOffset={alignOffset}
         side={side}
         sideOffset={sideOffset}
+        className="isolate z-dropdown"
       >
         <SelectPrimitive.Popup
           data-slot="select-content"
diff --git a/web/tests/select.test.tsx b/web/tests/select.test.tsx
new file mode 100644
index 00000000..ab991beb
--- /dev/null
+++ b/web/tests/select.test.tsx
@@ -0,0 +1,32 @@
+import { fireEvent, render, screen } from "@testing-library/react";
+import { describe, expect, it } from "vitest";
+import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from "@/components/ui/select";
+
+describe("Select", () => {
+  it("places the positioner in the dropdown stacking layer", () => {
+    const items = [
+      { value: "create_time", label: "Created" },
+      { value: "update_time", label: "Last updated" },
+    ];
+    render(
+      <Select defaultValue="update_time" items={items}>
+        <SelectTrigger aria-label="Shown time">
+          <SelectValue />
+        </SelectTrigger>
+        <SelectContent>
+          {items.map((item) => (
+            <SelectItem key={item.value} value={item.value}>
+              {item.label}
+            </SelectItem>
+          ))}
+        </SelectContent>
+      </Select>,
+    );
+
+    fireEvent.click(screen.getByRole("combobox", { name: "Shown time" }));
+
+    const popup = document.querySelector('[data-slot="select-content"]');
+    expect(popup).not.toBeNull();
+    expect(popup?.parentElement).toHaveClass("isolate", "z-dropdown");
+  });
+});