diff -r 5dc02b23752f -r 3e2da88830cd src/corelib/io/qiodevice.cpp
--- a/src/corelib/io/qiodevice.cpp	Tue Jul 06 15:10:48 2010 +0300
+++ b/src/corelib/io/qiodevice.cpp	Wed Aug 18 10:37:55 2010 +0300
@@ -1442,6 +1442,35 @@
     return q_func()->write(&c, 1) == 1;
 }
 
+/*!
+    \internal
+*/
+qint64 QIODevicePrivate::peek(char *data, qint64 maxSize)
+{
+    qint64 readBytes = q_func()->read(data, maxSize);
+    if (readBytes <= 0)
+        return readBytes;
+
+    buffer.ungetBlock(data, readBytes);
+    *pPos -= readBytes;
+    return readBytes;
+}
+
+/*!
+    \internal
+*/
+QByteArray QIODevicePrivate::peek(qint64 maxSize)
+{
+    QByteArray result = q_func()->read(maxSize);
+
+    if (result.isEmpty())
+        return result;
+
+    buffer.ungetBlock(result.constData(), result.size());
+    *pPos -= result.size();
+    return result;
+}
+
 /*! \fn bool QIODevice::getChar(char *c)
 
     Reads one character from the device and stores it in \a c. If \a c
@@ -1476,11 +1505,7 @@
 */
 qint64 QIODevice::peek(char *data, qint64 maxSize)
 {
-    qint64 readBytes = read(data, maxSize);
-    int i = readBytes;
-    while (i > 0)
-        ungetChar(data[i-- - 1]);
-    return readBytes;
+    return d_func()->peek(data, maxSize);
 }
 
 /*!
@@ -1502,12 +1527,7 @@
 */
 QByteArray QIODevice::peek(qint64 maxSize)
 {
-    QByteArray result = read(maxSize);
-    int i = result.size();
-    const char *data = result.constData();
-    while (i > 0)
-        ungetChar(data[i-- - 1]);
-    return result;
+    return d_func()->peek(maxSize);
 }
 
 /*!