diff --git a/poi/src/test/java/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java b/poi/src/test/java/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java
index 5302595a70..b164c9ef0e 100644
--- a/poi/src/test/java/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java
+++ b/poi/src/test/java/org/apache/poi/ss/formula/atp/TestWorkdayCalculator.java
@@ -87,9 +87,17 @@ class TestWorkdayCalculator {
 
     @Test
     void testCalculateWorkdaysNumberOfDays() {
-        double start = 41553.0;
+        double start = DateUtil.getExcelDate(d(2013, 10, 4));
+        assertEquals(41551.0, start);
         int days = 1;
         assertEquals(d(2013, 10, 7), WorkdayCalculator.instance.calculateWorkdays(start, days, new double[0]));
+        assertEquals(d(2013, 10, 7), WorkdayCalculator.instance.calculateWorkdays(start + 1, days, new double[0]));
+        assertEquals(d(2013, 10, 7), WorkdayCalculator.instance.calculateWorkdays(start + 2, days, new double[0]));
+        assertEquals(d(2013, 10, 5),
+                WorkdayCalculator.instance.calculateWorkdays(start, days, 5, new double[0]));
+
+        assertEquals(d(2013, 10, 3), WorkdayCalculator.instance.calculateWorkdays(start, -1, new double[0]));
+
     }
 
     @Test