diff --git a/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java b/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java
index ce56b6a6d6..e3afdc5c02 100644
--- a/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java
+++ b/src/ooxml/java/org/apache/poi/xssf/streaming/SXSSFWorkbook.java
@@ -331,7 +331,7 @@ public class SXSSFWorkbook implements Workbook
             ZipOutputStream zos = new ZipOutputStream(out);
             try
             {
-                Enumeration<ZipEntry> en = (Enumeration<ZipEntry>) zip.entries();
+                Enumeration<? extends ZipEntry> en = zip.entries();
                 while (en.hasMoreElements()) 
                 {
                     ZipEntry ze = en.nextElement();