--- a/src/corelib/kernel/qabstractitemmodel.cpp	Fri Feb 19 23:40:16 2010 +0200
+++ b/src/corelib/kernel/qabstractitemmodel.cpp	Fri Mar 12 15:46:37 2010 +0200
@@ -1006,6 +1006,9 @@
     Returns the child of the model index that is stored in the given \a row and
     \a column.
 
+    \note This function does not work for an invalid model index which is often
+    used as the root index.
+
     \sa parent(), sibling()
 */