diff --git a/src/ooxml/java/org/apache/poi/ss/usermodel/WorkbookFactory.java b/src/ooxml/java/org/apache/poi/ss/usermodel/WorkbookFactory.java
index b17a1a5aa5..dae4ff36ed 100644
--- a/src/ooxml/java/org/apache/poi/ss/usermodel/WorkbookFactory.java
+++ b/src/ooxml/java/org/apache/poi/ss/usermodel/WorkbookFactory.java
@@ -105,6 +105,7 @@ public class WorkbookFactory {
             NPOIFSFileSystem fs = new NPOIFSFileSystem(file);
             return new HSSFWorkbook(fs.getRoot(), true);
         } catch(OfficeXmlFileException e) {
+            // opening as .xls failed => try opening as .xlsx
             OPCPackage pkg = OPCPackage.open(file);
             return new XSSFWorkbook(pkg);
         }