diff --git a/comphelper/source/streaming/memorystream.cxx b/comphelper/source/streaming/memorystream.cxx
index 3afd9b555a84..9e209a01c581 100644
--- a/comphelper/source/streaming/memorystream.cxx
+++ b/comphelper/source/streaming/memorystream.cxx
@@ -35,15 +35,16 @@
 
 #include <com/sun/star/io/XStream.hpp>
 #include <com/sun/star/io/XSeekableInputStream.hpp>
+#include <com/sun/star/io/XTruncate.hpp>
 #include <com/sun/star/uno/XComponentContext.hpp>
-#include <cppuhelper/implbase3.hxx>
+#include <cppuhelper/implbase4.hxx>
 
 #include <string.h>
 #include <vector>
 
 using ::rtl::OUString;
 using ::cppu::OWeakObject;
-using ::cppu::WeakImplHelper3;
+using ::cppu::WeakImplHelper4;
 using namespace ::com::sun::star::io;
 using namespace ::com::sun::star::uno;
 using namespace ::com::sun::star::lang;
@@ -52,7 +53,7 @@ using namespace ::osl;
 namespace comphelper
 {
 
-class UNOMemoryStream : public WeakImplHelper3 < XStream, XSeekableInputStream, XOutputStream >
+class UNOMemoryStream : public WeakImplHelper4 < XStream, XSeekableInputStream, XOutputStream, XTruncate >
 {
 public:
     UNOMemoryStream();
@@ -79,6 +80,9 @@ public:
     virtual void SAL_CALL flush() throw (NotConnectedException, BufferSizeExceededException, IOException, RuntimeException);
     virtual void SAL_CALL closeOutput() throw (NotConnectedException, BufferSizeExceededException, IOException, RuntimeException);
 
+    // XTruncate
+    virtual void SAL_CALL truncate() throw (::com::sun::star::io::IOException, ::com::sun::star::uno::RuntimeException);
+
     // XServiceInfo - static versions (used for component registration)
     static ::rtl::OUString SAL_CALL getImplementationName_static();
     static Sequence< ::rtl::OUString > SAL_CALL getSupportedServiceNames_static();
@@ -116,8 +120,7 @@ sal_Int32 SAL_CALL UNOMemoryStream::readBytes( Sequence< sal_Int8 >& aData, sal_
         throw IOException();
 
     nBytesToRead = std::min( nBytesToRead, available() );
-    if( aData.getLength() < nBytesToRead )
-        aData.realloc( nBytesToRead );
+    aData.realloc( nBytesToRead );
 
     if( nBytesToRead )
     {
@@ -157,9 +160,12 @@ void SAL_CALL UNOMemoryStream::closeInput() throw (NotConnectedException, IOExce
 // XSeekable
 void SAL_CALL UNOMemoryStream::seek( sal_Int64 location ) throw (IllegalArgumentException, IOException, RuntimeException)
 {
-    if( (location < 0) || (location > SAL_MAX_INT32) || (location > static_cast< sal_Int64 >( maData.size() )) )
+    if( (location < 0) || (location > SAL_MAX_INT32) )
         throw IllegalArgumentException( OUString(RTL_CONSTASCII_USTRINGPARAM("this implementation does not support more than 2GB!")), Reference< XInterface >(static_cast<OWeakObject*>(this)), 0 );
 
+    if ( location > static_cast< sal_Int64 >( maData.size() ) )
+        maData.resize( static_cast< sal_Int32 >( location ) );
+
     mnCursor = static_cast< sal_Int32 >( location );
 }
 
@@ -206,6 +212,13 @@ void SAL_CALL UNOMemoryStream::closeOutput() throw (NotConnectedException, Buffe
     mnCursor = 0;
 }
 
+//XTruncate
+void SAL_CALL UNOMemoryStream::truncate() throw (IOException, RuntimeException)
+{
+    maData.resize( 0 );
+    mnCursor = 0;
+}
+
 ::rtl::OUString SAL_CALL UNOMemoryStream::getImplementationName_static()
 {
     static const OUString sImplName( RTL_CONSTASCII_USTRINGPARAM( "com.sun.star.comp.MemoryStream" ) );