diff --git a/src/getOverlappingDaysInIntervals/index.ts b/src/getOverlappingDaysInIntervals/index.ts
index ab50ef14e5..22e3ceccc6 100644
--- a/src/getOverlappingDaysInIntervals/index.ts
+++ b/src/getOverlappingDaysInIntervals/index.ts
@@ -41,11 +41,11 @@ export function getOverlappingDaysInIntervals<DateType extends Date>(
   const [leftStartTime, leftEndTime] = [
     +toDate(intervalLeft.start),
     +toDate(intervalLeft.end),
-  ].sort();
+  ].sort((a, b) => a - b);
   const [rightStartTime, rightEndTime] = [
     +toDate(intervalRight.start),
     +toDate(intervalRight.end),
-  ].sort();
+  ].sort((a, b) => a - b);
 
   const isOverlapping =
     leftStartTime < rightEndTime && rightStartTime < leftEndTime;
diff --git a/src/getOverlappingDaysInIntervals/test.ts b/src/getOverlappingDaysInIntervals/test.ts
index 21201fde08..1dad0b91ba 100644
--- a/src/getOverlappingDaysInIntervals/test.ts
+++ b/src/getOverlappingDaysInIntervals/test.ts
@@ -1,7 +1,7 @@
 /* eslint-env mocha */
 
 import assert from "assert";
-import { describe, it } from "vitest";
+import { describe, expect, it } from "vitest";
 import { getOverlappingDaysInIntervals } from "./index.js";
 
 describe("getOverlappingDaysInIntervals", () => {
@@ -214,4 +214,18 @@ describe("getOverlappingDaysInIntervals", () => {
       assert(numOverlappingDays === 0);
     });
   });
+
+  it("properly sorts the dates", () => {
+    const result = getOverlappingDaysInIntervals(
+      {
+        start: new Date(2001, 8 /* Sep */, 1),
+        end: new Date(2023, 11 /* Dec */, 20),
+      },
+      {
+        start: new Date(2023, 11 /* Dec */, 21),
+        end: new Date(2001, 8 /* Sep */, 9),
+      },
+    );
+    expect(result).toBe(8137);
+  });
 });