diff --git a/.changeset/anchor-links-same-tab.md b/.changeset/anchor-links-same-tab.md
new file mode 100644
index 0000000000..0c7e4b0ec1
--- /dev/null
+++ b/.changeset/anchor-links-same-tab.md
@@ -0,0 +1,5 @@
+---
+"emdash": patch
+---
+
+Fixes same-page anchor links (e.g. `#section`) in Portable Text content opening in a new tab. On-page jumps now always stay in the same tab, even when the link's "open in new window" option is set.
diff --git a/packages/core/src/components/marks/Link.astro b/packages/core/src/components/marks/Link.astro
index 130a661a3b..7fdcbf0fbb 100644
--- a/packages/core/src/components/marks/Link.astro
+++ b/packages/core/src/components/marks/Link.astro
@@ -19,7 +19,11 @@ export interface Props {
 
 const { node } = Astro.props;
 const href = sanitizeHref(node?.markDef?.href);
-const blank = node?.markDef?.blank;
+// Same-page anchor links (`#section`) are on-page jumps — opening them in a
+// new tab is never desirable, so force same-tab regardless of the mark's
+// `blank` flag.
+const isSamePageAnchor = href.startsWith("#");
+const blank = !isSamePageAnchor && node?.markDef?.blank;
 ---
 
 <a
diff --git a/packages/core/tests/repro/link-mark-anchor.render.test.ts b/packages/core/tests/repro/link-mark-anchor.render.test.ts
new file mode 100644
index 0000000000..0a33f98004
--- /dev/null
+++ b/packages/core/tests/repro/link-mark-anchor.render.test.ts
@@ -0,0 +1,61 @@
+/**
+ * Same-page anchor links (`#section`) must never open in a new tab, even when
+ * the stored link mark has `blank: true`. Opening an on-page jump in a new tab
+ * is never desirable — it should stay in the same tab (`_self`).
+ *
+ * Regression: external links with `blank: true` must still open in a new tab.
+ */
+import { experimental_AstroContainer as AstroContainer } from "astro/container";
+import { describe, expect, test } from "vitest";
+
+import Link from "../../src/components/marks/Link.astro";
+
+const anchorTag = (html: string) => html.match(/<a\b[^>]*>/)?.[0] ?? "";
+
+async function renderLink(markDef: Record<string, unknown>) {
+	const c = await AstroContainer.create();
+	return c.renderToString(Link, {
+		props: { node: { markDef } },
+		slots: { default: "jump" },
+	});
+}
+
+describe("Link mark: same-page anchor target handling", () => {
+	test("same-page anchor with blank=true stays in same tab", async () => {
+		const html = await renderLink({
+			_type: "link",
+			_key: "k1",
+			href: "#section",
+			blank: true,
+		});
+		const tag = anchorTag(html);
+		expect(tag).toContain('href="#section"');
+		expect(tag).not.toContain('target="_blank"');
+		expect(tag).not.toContain("noopener");
+	});
+
+	test("external link with blank=true still opens in new tab", async () => {
+		const html = await renderLink({
+			_type: "link",
+			_key: "k2",
+			href: "https://example.com",
+			blank: true,
+		});
+		const tag = anchorTag(html);
+		expect(tag).toContain('href="https://example.com"');
+		expect(tag).toContain('target="_blank"');
+		expect(tag).toContain("noopener");
+	});
+
+	test("same-page anchor without blank stays in same tab", async () => {
+		const html = await renderLink({
+			_type: "link",
+			_key: "k3",
+			href: "#top",
+			blank: false,
+		});
+		const tag = anchorTag(html);
+		expect(tag).toContain('href="#top"');
+		expect(tag).not.toContain('target="_blank"');
+	});
+});