diff --git a/python/plugins/fTools/tools/doGeometry.py b/python/plugins/fTools/tools/doGeometry.py
index 12c6ffe50337..d2441541437c 100644
--- a/python/plugins/fTools/tools/doGeometry.py
+++ b/python/plugins/fTools/tools/doGeometry.py
@@ -232,6 +232,14 @@ def geometry( self, myLayer, myParam, myField ):
       self.shapefileName = None
       self.encoding = None
 
+      res = QMessageBox.warning( self, self.tr( "Geometry"),
+                                 self.tr( "Currently QGIS doesn't allow simultaneous access from \
+                                 different threads to the same datasource. Make sure your layer's \
+                                 attribute tables are closed. Continue?"),
+                                 QMessageBox.Yes | QMessageBox.No )
+      if res == QMessageBox.No:
+        return
+
     self.buttonOk.setEnabled( False )
     self.testThread = geometryThread( self.iface.mainWindow(), self, self.myFunction,
                                       vlayer, myParam, myField, self.shapefileName, self.encoding,
diff --git a/python/plugins/fTools/tools/doSimplify.py b/python/plugins/fTools/tools/doSimplify.py
index 276e233cdb7c..025d234999c7 100644
--- a/python/plugins/fTools/tools/doSimplify.py
+++ b/python/plugins/fTools/tools/doSimplify.py
@@ -104,6 +104,14 @@ def accept( self ):
       self.workThread = GeomThread( self.myFunction, vLayer, self.chkUseSelection.isChecked(),
                                     self.spnTolerance.value(), True, outFileName, self.encoding )
     else:
+      res = QMessageBox.warning( self, self.tr( "Warning"),
+                                 self.tr( "Currently QGIS doesn't allow simultaneous access from \
+                                 different threads to the same datasource. Make sure your layer's \
+                                 attribute tables are closed. Continue?"),
+                                 QMessageBox.Yes | QMessageBox.No )
+      if res == QMessageBox.No:
+        return
+
       self.workThread = GeomThread( self.myFunction, vLayer, self.chkUseSelection.isChecked(),
                                     self.spnTolerance.value(), False, None, None )