diff --git a/src/testcases/org/apache/poi/ss/usermodel/TestDataFormatter.java b/src/testcases/org/apache/poi/ss/usermodel/TestDataFormatter.java
index d98133de1..b7990b43f 100644
--- a/src/testcases/org/apache/poi/ss/usermodel/TestDataFormatter.java
+++ b/src/testcases/org/apache/poi/ss/usermodel/TestDataFormatter.java
@@ -862,7 +862,7 @@ public class TestDataFormatter {
         try {
             char euro = '\u20AC';
             DataFormatter df = new DataFormatter(Locale.GERMANY);
-            String formatString = String.format(
+            String formatString = String.format(Locale.ROOT,
                     "_-* #,##0.00\\ \"%s\"_-;\\-* #,##0.00\\ \"%s\"_-;_-* \"-\"??\\ \"%s\"_-;_-@_-",
                     euro, euro, euro);
             assertEquals("4.33 " + euro, df.formatRawCellContents(4.33, 178, formatString));