diff --git a/autotests/kcompressiondevicetest.h b/autotests/kcompressiondevicetest.h
--- a/autotests/kcompressiondevicetest.h
+++ b/autotests/kcompressiondevicetest.h
@@ -57,6 +57,8 @@
 
     void testWriteErrorOnOpen();
     void testWriteErrorOnClose();
+
+    void testSeekReadUncompressedBuffer();
 };
 
 #endif
diff --git a/autotests/kcompressiondevicetest.cpp b/autotests/kcompressiondevicetest.cpp
--- a/autotests/kcompressiondevicetest.cpp
+++ b/autotests/kcompressiondevicetest.cpp
@@ -18,6 +18,7 @@
 */
 
 #include "kcompressiondevicetest.h"
+#include "kcompressiondevice_p.h"
 
 #include <config-compression.h>
 
@@ -190,3 +191,29 @@
     // THEN
     QCOMPARE(int(dev.error()), int(QFileDevice::WriteError));
 }
+
+void KCompressionDeviceTest::testSeekReadUncompressedBuffer()
+{
+    const int dataSize = BUFFER_SIZE + BUFFER_SIZE / 2;
+    QByteArray ba(dataSize, 0);
+
+    // all data is zero except after BUFFER_SIZE that it's 0 to 9
+    for (int i = 0; i < 10; ++i) {
+        ba[BUFFER_SIZE + i] = i;
+    }
+
+    QBuffer b;
+    b.setData(ba);
+    QVERIFY(b.open(QIODevice::ReadOnly));
+
+    KCompressionDevice kcd(&b, false, KCompressionDevice::GZip);
+    QVERIFY(kcd.open(QIODevice::ReadOnly));
+    QVERIFY(kcd.seek(BUFFER_SIZE));
+
+    // the 10 bytes after BUFFER_SIZE should be 0 to 9
+    const QByteArray kcdData = kcd.read(10);
+    QCOMPARE(kcdData.size(), 10);
+    for (int i = 0; i < kcdData.size(); ++i) {
+        QCOMPARE(kcdData[i], i);
+    }
+}
diff --git a/src/kcompressiondevice.cpp b/src/kcompressiondevice.cpp
--- a/src/kcompressiondevice.cpp
+++ b/src/kcompressiondevice.cpp
@@ -18,6 +18,7 @@
 */
 
 #include "kcompressiondevice.h"
+#include "kcompressiondevice_p.h"
 #include "loggingcategory.h"
 #include <config-compression.h>
 #include "kfilterbase.h"
@@ -36,8 +37,6 @@
 #include "kxzfilter.h"
 #endif
 
-#define BUFFER_SIZE 8*1024
-
 #include <QDebug>
 
 class KCompressionDevicePrivate
diff --git a/src/kcompressiondevice_p.h b/src/kcompressiondevice_p.h
new file mode 100644
--- /dev/null
+++ b/src/kcompressiondevice_p.h
@@ -0,0 +1,24 @@
+/* This file is part of the KDE libraries
+   Copyright (C) 2000 David Faure <faure@kde.org>
+   Copyright (C) 2011 Mario Bensi <mbensi@ipsquad.net>
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public
+   License version 2 as published by the Free Software Foundation.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public License
+   along with this library; see the file COPYING.LIB.  If not, write to
+   the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   Boston, MA 02110-1301, USA.
+*/
+#ifndef __kcompressiondevice_p_h
+#define __kcompressiondevice_p_h
+
+#define BUFFER_SIZE 8*1024
+
+#endif