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diff --git a/date-fns/src/addDays/index.ts b/date-fns/src/addDays/index.ts
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+import toInteger from '../_lib/toInteger/index'
+import toDate from '../toDate/index'
+import requiredArgs from '../_lib/requiredArgs/index'
+
+/**
+ * @name addDays
+ * @category Day Helpers
+ * @summary Add the specified number of days to the given date.
+ *
+ * @description
+ * Add the specified number of days to the given date.
+ *
+ * ### v2.0.0 breaking changes:
+ *
+ * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
+ *
+ * @param {Date|Number} date - the date to be changed
+ * @param {Number} amount - the amount of days to be added. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
+ * @returns {Date} - the new date with the days added
+ * @throws {TypeError} - 2 arguments required
+ *
+ * @example
+ * // Add 10 days to 1 September 2014:
+ * const result = addDays(new Date(2014, 8, 1), 10)
+ * //=> Thu Sep 11 2014 00:00:00
+ */
+export default function addDays(
+  dirtyDate: Date | number,
+  dirtyAmount: number
+): Date {
+  requiredArgs(2, arguments)
+
+  const date = toDate(dirtyDate)
+  const amount = toInteger(dirtyAmount)
+  if (isNaN(amount)) {
+    return new Date(NaN)
+  }
+  if (!amount) {
+    // If 0 days, no-op to avoid changing times in the hour before end of DST
+    return date
+  }
+  date.setDate(date.getDate() + amount)
+  return date
+}