Index: xstream/src/java/com/thoughtworks/xstream/core/util/XmlHeaderAwareReader.java
===================================================================
--- xstream/src/java/com/thoughtworks/xstream/core/util/XmlHeaderAwareReader.java	(revision 1488)
+++ xstream/src/java/com/thoughtworks/xstream/core/util/XmlHeaderAwareReader.java	(working copy)
@@ -54,9 +54,7 @@
      * @since 1.3
      */
     public XmlHeaderAwareReader(final InputStream in) throws UnsupportedEncodingException, IOException {
-        final PushbackInputStream pin = in instanceof PushbackInputStream
-                                                                         ? (PushbackInputStream)in
-                                                                         : new PushbackInputStream(in, 64);
+        final PushbackInputStream pin = new PushbackInputStream(in, 64);
         final Map header = getHeader(pin);
         version = Double.parseDouble((String)header.get(KEY_VERSION));
         reader = new InputStreamReader(pin, (String)header.get(KEY_ENCODING));
Index: xstream/src/test/com/thoughtworks/xstream/core/util/XmlHeaderAwareReaderTest.java
===================================================================
--- xstream/src/test/com/thoughtworks/xstream/core/util/XmlHeaderAwareReaderTest.java	(revision 1488)
+++ xstream/src/test/com/thoughtworks/xstream/core/util/XmlHeaderAwareReaderTest.java	(working copy)
@@ -12,8 +12,10 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.io.LineNumberReader;
+import java.io.PushbackInputStream;
 
 import junit.framework.TestCase;
 
@@ -54,4 +56,10 @@
         XmlHeaderAwareReader reader = new XmlHeaderAwareReader(in);
         assertEquals(1.1, reader.getVersion(), 0.001);
     }
+    
+    public void testReadFromPreexistingPushbackInputStream() throws IOException {
+        InputStream in = new PushbackInputStream(new ByteArrayInputStream("<?xml version='1.\\1' ?>".getBytes("us-ascii")), 1);
+        XmlHeaderAwareReader reader = new XmlHeaderAwareReader(in);
+        assertEquals(1.1, reader.getVersion(), 0.001);
+    }
 }