diff -r 89e065397ea6 -r e24348a560a6 src/corelib/io/qiodevice.cpp
--- a/src/corelib/io/qiodevice.cpp	Thu May 27 13:40:48 2010 +0300
+++ b/src/corelib/io/qiodevice.cpp	Fri Jun 11 14:24:45 2010 +0300
@@ -810,6 +810,9 @@
                 }
             }
 
+            if (!maxSize)
+                return readSoFar;
+
             if ((d->openMode & Unbuffered) == 0 && maxSize < QIODEVICE_BUFFERSIZE) {
                 // In buffered mode, we try to fill up the QIODevice buffer before
                 // we do anything else.