diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index a60aee1ebe..07634c3ca2 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -789,8 +789,10 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
             readSoFar += lastReadChunkSize;
             // fast exit when satisfied by buffer
             if (lastReadChunkSize == maxSize && !(d->openMode & Text)) {
-                if (d->buffer.isEmpty())
+                if (d->buffer.isEmpty()) {
+                    d->buffer.clear();
                     readData(data, 0);
+                }
                 return readSoFar;
             }
 
diff --git a/src/corelib/io/qiodevice_p.h b/src/corelib/io/qiodevice_p.h
index 4819ec11a0..362ea4bdf0 100644
--- a/src/corelib/io/qiodevice_p.h
+++ b/src/corelib/io/qiodevice_p.h
@@ -78,8 +78,11 @@ public:
         delete [] buf;
     }
     void clear() {
-        first = buf;
         len = 0;
+        delete [] buf;
+        buf = 0;
+        first = buf;
+        capacity = 0;
     }
     int size() const {
         return len;
@@ -129,10 +132,9 @@ public:
         }
     }
     QByteArray readAll() {
-        char* f = first;
-        int l = len;
+        QByteArray retVal(first, len);
         clear();
-        return QByteArray(f, l);
+        return retVal;
     }
     int readLine(char* target, int size) {
         int r = qMin(size, len);