diff --git a/main/pom.xml b/main/pom.xml
index 99c673bf3..bfb3b76cc 100644
--- a/main/pom.xml
+++ b/main/pom.xml
@@ -348,12 +348,12 @@
     <dependency>
       <groupId>org.apache.poi</groupId>
       <artifactId>poi</artifactId>
-      <version>4.0.1</version>
+      <version>4.1.0</version>
     </dependency>
     <dependency>
       <groupId>org.apache.poi</groupId>
       <artifactId>poi-ooxml</artifactId>
-      <version>3.8</version> <!-- in classpath: 3.13-20150929 -->
+      <version>4.1.0</version> <!-- in classpath: 3.13-20150929 -->
     </dependency>
     <dependency>
       <groupId>org.apache.odftoolkit</groupId>
diff --git a/main/src/com/google/refine/exporters/XlsExporter.java b/main/src/com/google/refine/exporters/XlsExporter.java
index 3dbce9de0..b1749d9d1 100644
--- a/main/src/com/google/refine/exporters/XlsExporter.java
+++ b/main/src/com/google/refine/exporters/XlsExporter.java
@@ -141,6 +141,7 @@ public class XlsExporter implements StreamExporter {
                 project, engine, params, serializer);
         
         wb.write(outputStream);
+        wb.close();
         outputStream.flush();
     }
 
diff --git a/main/src/com/google/refine/importers/ExcelImporter.java b/main/src/com/google/refine/importers/ExcelImporter.java
index 4ce4d4792..cace15770 100644
--- a/main/src/com/google/refine/importers/ExcelImporter.java
+++ b/main/src/com/google/refine/importers/ExcelImporter.java
@@ -44,8 +44,8 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import org.apache.poi.POIXMLDocument;
-import org.apache.poi.POIXMLException;
+import org.apache.poi.ooxml.POIXMLDocument;
+import org.apache.poi.ooxml.POIXMLException;
 import org.apache.poi.common.usermodel.Hyperlink;
 import org.apache.poi.hssf.usermodel.HSSFDateUtil;
 import org.apache.poi.hssf.usermodel.HSSFWorkbook;
@@ -95,7 +95,7 @@ public class ExcelImporter extends TabularImportingParserBase {
                 }
 
                 try {
-                    Workbook wb = POIXMLDocument.hasOOXMLHeader(is) ?
+                    Workbook wb = FileMagic.valueOf(is) == FileMagic.OOXML ?
                             new XSSFWorkbook(is) :
                                 new HSSFWorkbook(new POIFSFileSystem(is));
 
@@ -147,7 +147,7 @@ public class ExcelImporter extends TabularImportingParserBase {
         }
         
         try {
-            wb = POIXMLDocument.hasOOXMLHeader(inputStream) ?
+            wb = FileMagic.valueOf(InputStream) == FileMagic.OOXML ?
                 new XSSFWorkbook(inputStream) :
                 new HSSFWorkbook(new POIFSFileSystem(inputStream));
         } catch (IOException e) {