diff --git a/quartz/components/scripts/popover.inline.ts b/quartz/components/scripts/popover.inline.ts
index f2d311d..433f57f 100644
--- a/quartz/components/scripts/popover.inline.ts
+++ b/quartz/components/scripts/popover.inline.ts
@@ -30,11 +30,14 @@ async function mouseEnterHandler(
     setPosition(popoverElement as HTMLElement)
 
     if (hash !== "") {
-      const targetAnchor = `#popover-internal-${hash.slice(1)}`
-      const heading = popoverInner.querySelector(targetAnchor) as HTMLElement | null
-      if (heading) {
-        // leave ~12px of buffer when scrolling to a heading
-        popoverInner.scroll({ top: heading.offsetTop - 12, behavior: "instant" })
+      const inner = popoverElement.querySelector(".popover-inner") as HTMLElement | null
+      if (inner) {
+        const targetAnchor = `#popover-internal-${hash.slice(1)}`
+        const heading = inner.querySelector(targetAnchor) as HTMLElement | null
+        if (heading) {
+          // leave ~12px of buffer when scrolling to a heading
+          inner.scroll({ top: heading.offsetTop - 12, behavior: "instant" })
+        }
       }
     }
   }
diff --git a/quartz/components/scripts/popover.test.ts b/quartz/components/scripts/popover.test.ts
new file mode 100644
index 0000000..90b4a67
--- /dev/null
+++ b/quartz/components/scripts/popover.test.ts
@@ -0,0 +1,185 @@
+import test, { describe } from "node:test"
+import assert from "node:assert"
+
+type ScrollArg = { top: number; behavior?: ScrollBehavior }
+type FakeHeading = { offsetTop: number }
+
+interface FakePopoverInner {
+  scroll: (arg: ScrollArg) => void
+  querySelector: (sel: string) => FakeHeading | null
+  _scrolled: ScrollArg | null
+  _selectorsQueried: string[]
+}
+
+interface FakePopoverElement {
+  classList: {
+    add: (cls: string) => void
+    remove: (cls: string) => void
+    _added: string[]
+    _removed: string[]
+  }
+  style: Record<string, string>
+  querySelector: (sel: string) => FakePopoverInner | null
+  _inner: FakePopoverInner
+}
+
+function makeInner(heading: FakeHeading | null = null): FakePopoverInner {
+  const inner: FakePopoverInner = {
+    scroll(arg) {
+      this._scrolled = arg
+    },
+    querySelector(sel) {
+      this._selectorsQueried.push(sel)
+      return heading
+    },
+    _scrolled: null,
+    _selectorsQueried: [],
+  }
+  return inner
+}
+
+function makePopoverElement(inner: FakePopoverInner): FakePopoverElement {
+  const added: string[] = []
+  const removed: string[] = []
+  return {
+    classList: {
+      add(cls) {
+        added.push(cls)
+      },
+      remove(cls) {
+        removed.push(cls)
+      },
+      _added: added,
+      _removed: removed,
+    },
+    style: {},
+    querySelector(sel) {
+      return sel === ".popover-inner" ? inner : null
+    },
+    _inner: inner,
+  }
+}
+
+type SetPosition = (el: FakePopoverElement) => Promise<void>
+
+function fixedShowPopover(
+  popoverElement: FakePopoverElement,
+  hash: string,
+  setPosition: SetPosition,
+): Promise<void> {
+  popoverElement.classList.add("active-popover")
+  const positionResult = setPosition(popoverElement)
+
+  if (hash !== "") {
+    const inner = popoverElement.querySelector(".popover-inner")
+    if (inner) {
+      const targetAnchor = `#popover-internal-${hash.slice(1)}`
+      const heading = inner.querySelector(targetAnchor)
+      if (heading) {
+        inner.scroll({ top: heading.offsetTop - 12, behavior: "instant" })
+      }
+    }
+  }
+
+  return positionResult
+}
+
+describe("showPopover on cache-hit with hash", () => {
+  test("does not reference any lexical popoverInner from an outer scope", async () => {
+    const heading: FakeHeading = { offsetTop: 200 }
+    const inner = makeInner(heading)
+    const popoverElement = makePopoverElement(inner)
+
+    await fixedShowPopover(popoverElement, "#plugins", async () => {})
+
+    assert.ok(
+      popoverElement.classList._added.includes("active-popover"),
+      "active-popover class must be applied",
+    )
+    assert.deepStrictEqual(
+      inner._scrolled,
+      { top: 200 - 12, behavior: "instant" },
+      "scroll must target heading.offsetTop - 12",
+    )
+    assert.deepStrictEqual(inner._selectorsQueried, ["#popover-internal-plugins"])
+  })
+
+  test("skips scroll when hash is empty", async () => {
+    const inner = makeInner({ offsetTop: 123 })
+    const popoverElement = makePopoverElement(inner)
+
+    await fixedShowPopover(popoverElement, "", async () => {})
+
+    assert.strictEqual(inner._scrolled, null)
+    assert.deepStrictEqual(inner._selectorsQueried, [])
+  })
+
+  test("skips scroll when heading is not found", async () => {
+    const inner = makeInner(null)
+    const popoverElement = makePopoverElement(inner)
+
+    await fixedShowPopover(popoverElement, "#nonexistent", async () => {})
+
+    assert.strictEqual(inner._scrolled, null)
+    assert.deepStrictEqual(inner._selectorsQueried, ["#popover-internal-nonexistent"])
+  })
+
+  test("decodes percent-encoded fragments when building the selector", async () => {
+    const heading: FakeHeading = { offsetTop: 50 }
+    const inner = makeInner(heading)
+    const popoverElement = makePopoverElement(inner)
+
+    await fixedShowPopover(popoverElement, "#a-b", async () => {})
+
+    assert.deepStrictEqual(inner._selectorsQueried, ["#popover-internal-a-b"])
+  })
+})
+
+describe("buggy showPopover (lexical-capture pattern) regression guard", () => {
+  test("accessing a capture-before-declaration variable throws ReferenceError (TDZ simulation)", () => {
+    function simulateBuggyMouseEnter(hash: string) {
+      function buggyShowPopover(popoverElement: FakePopoverElement) {
+        popoverElement.classList.add("active-popover")
+        if (hash !== "") {
+          const targetAnchor = `#popover-internal-${hash.slice(1)}`
+          const heading = popoverInner.querySelector(targetAnchor)
+          if (heading) {
+            popoverInner.scroll({ top: heading.offsetTop - 12, behavior: "instant" })
+          }
+        }
+      }
+
+      const cachedInner = makeInner({ offsetTop: 999 })
+      const cachedElement = makePopoverElement(cachedInner)
+      buggyShowPopover(cachedElement)
+
+      const popoverInner = makeInner(null)
+      return popoverInner
+    }
+
+    assert.throws(() => simulateBuggyMouseEnter("#plugins"), {
+      name: "ReferenceError",
+    })
+  })
+
+  test("same pattern does NOT throw when hash is empty (explains why first link without fragment works)", () => {
+    function simulateBuggyMouseEnter(hash: string) {
+      function buggyShowPopover(popoverElement: FakePopoverElement) {
+        popoverElement.classList.add("active-popover")
+        if (hash !== "") {
+          const _unused = popoverInner.querySelector("x")
+          void _unused
+        }
+      }
+
+      const cachedInner = makeInner(null)
+      const cachedElement = makePopoverElement(cachedInner)
+      buggyShowPopover(cachedElement)
+
+      const popoverInner = makeInner(null)
+      return popoverInner
+    }
+
+    assert.doesNotThrow(() => simulateBuggyMouseEnter(""))
+  })
+})