diff --git a/test/date-sorting.test.ts b/test/date-sorting.test.ts
new file mode 100644
index 0000000..7c8cee7
--- /dev/null
+++ b/test/date-sorting.test.ts
@@ -0,0 +1,190 @@
+import { describe, expect, it } from "vitest";
+import { resolveDefaultDateType, withResolvedDateType } from "../src/index";
+import { byDateAndAlphabetical, getDate } from "@quartz-community/utils/sort";
+import type { FullSlug, GlobalConfiguration, QuartzPluginData } from "@quartz-community/types";
+
+function makePage(
+  slug: string,
+  title: string,
+  dates: { created: Date; modified: Date; published: Date },
+  defaultDateType?: string,
+): QuartzPluginData & Record<string, unknown> {
+  return {
+    slug: slug as FullSlug,
+    frontmatter: { title, tags: [] },
+    dates,
+    defaultDateType,
+  } as unknown as QuartzPluginData & Record<string, unknown>;
+}
+
+const jan = new Date("2025-01-15T00:00:00");
+const mar = new Date("2025-03-20T00:00:00");
+const may = new Date("2025-05-10T00:00:00");
+
+describe("resolveDefaultDateType", () => {
+  const cfgWithout = { locale: "en-US" } as GlobalConfiguration;
+  const cfgWith = { locale: "en-US", defaultDateType: "created" } as GlobalConfiguration & {
+    defaultDateType: string;
+  };
+
+  it("returns the per-file defaultDateType when set", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may }, "modified");
+    expect(resolveDefaultDateType(page, cfgWithout)).toBe("modified");
+  });
+
+  it("falls back to cfg.defaultDateType when per-file value is missing", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may });
+    expect(resolveDefaultDateType(page, cfgWith)).toBe("created");
+  });
+
+  it("returns undefined when neither per-file nor cfg has defaultDateType", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may });
+    expect(resolveDefaultDateType(page, cfgWithout)).toBeUndefined();
+  });
+
+  it("prefers per-file value over cfg value", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may }, "published");
+    expect(resolveDefaultDateType(page, cfgWith)).toBe("published");
+  });
+});
+
+describe("withResolvedDateType", () => {
+  const cfg = { locale: "en-US" } as GlobalConfiguration;
+
+  it("preserves per-file defaultDateType so getDate() works", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may }, "modified");
+    const resolved = withResolvedDateType(page, cfg);
+    const date = getDate(resolved);
+    expect(date).toEqual(mar);
+  });
+
+  it("does not overwrite per-file defaultDateType with undefined from cfg", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may }, "created");
+    const resolved = withResolvedDateType(page, cfg);
+    expect(resolved.defaultDateType).toBe("created");
+    expect(getDate(resolved)).toEqual(jan);
+  });
+
+  it("returns data as-is when no defaultDateType can be resolved", () => {
+    const page = makePage("a", "A", { created: jan, modified: mar, published: may });
+    const resolved = withResolvedDateType(page, cfg);
+    expect(getDate(resolved)).toBeUndefined();
+  });
+});
+
+describe("date sorting regression", () => {
+  const cfg = { locale: "en-US" } as GlobalConfiguration;
+
+  it("sorts by date descending when per-file defaultDateType is set (no cfg.defaultDateType)", () => {
+    const older = makePage(
+      "a",
+      "Alpha",
+      { created: jan, modified: jan, published: jan },
+      "modified",
+    );
+    const middle = makePage(
+      "b",
+      "Bravo",
+      { created: mar, modified: mar, published: mar },
+      "modified",
+    );
+    const newer = makePage(
+      "c",
+      "Charlie",
+      { created: may, modified: may, published: may },
+      "modified",
+    );
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [older, middle, newer].map((p) => withResolvedDateType(p, cfg)).sort(sortFn);
+
+    expect(pages.map((p) => p.slug)).toEqual(["c", "b", "a"]);
+  });
+
+  it("does not fall back to alphabetical when per-file dates exist", () => {
+    const olderButFirst = makePage(
+      "a",
+      "AAA",
+      { created: jan, modified: jan, published: jan },
+      "modified",
+    );
+    const newerButLast = makePage(
+      "b",
+      "ZZZ",
+      { created: may, modified: may, published: may },
+      "modified",
+    );
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [olderButFirst, newerButLast]
+      .map((p) => withResolvedDateType(p, cfg))
+      .sort(sortFn);
+
+    expect(pages.at(0)?.slug).toBe("b");
+    expect(pages.at(1)?.slug).toBe("a");
+  });
+
+  it("falls back to alphabetical only when no dates can be resolved", () => {
+    const pageZ = makePage("z", "Zulu", { created: jan, modified: mar, published: may });
+    const pageA = makePage("a", "Alpha", { created: jan, modified: mar, published: may });
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [pageZ, pageA].map((p) => withResolvedDateType(p, cfg)).sort(sortFn);
+
+    expect(pages.at(0)?.slug).toBe("a");
+    expect(pages.at(1)?.slug).toBe("z");
+  });
+
+  it("uses the correct date field based on defaultDateType", () => {
+    const createdOld = makePage(
+      "a",
+      "A",
+      { created: jan, modified: may, published: mar },
+      "created",
+    );
+    const createdNew = makePage(
+      "b",
+      "B",
+      { created: may, modified: jan, published: mar },
+      "created",
+    );
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [createdOld, createdNew].map((p) => withResolvedDateType(p, cfg)).sort(sortFn);
+
+    expect(pages.at(0)?.slug).toBe("b");
+    expect(pages.at(1)?.slug).toBe("a");
+  });
+
+  it("falls back to alphabetical only when no dates can be resolved", () => {
+    const pageZ = makePage("z", "Zulu", { created: jan, modified: mar, published: may });
+    const pageA = makePage("a", "Alpha", { created: jan, modified: mar, published: may });
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [pageZ, pageA].map((p) => withResolvedDateType(p, cfg)).sort(sortFn);
+
+    expect(pages.at(0)?.slug).toBe("a");
+    expect(pages.at(1)?.slug).toBe("z");
+  });
+
+  it("uses the correct date field based on defaultDateType", () => {
+    const createdOld = makePage(
+      "a",
+      "A",
+      { created: jan, modified: may, published: mar },
+      "created",
+    );
+    const createdNew = makePage(
+      "b",
+      "B",
+      { created: may, modified: jan, published: mar },
+      "created",
+    );
+
+    const sortFn = byDateAndAlphabetical();
+    const pages = [createdOld, createdNew].map((p) => withResolvedDateType(p, cfg)).sort(sortFn);
+
+    expect(pages.at(0)?.slug).toBe("b");
+    expect(pages.at(1)?.slug).toBe("a");
+  });
+});