diff --git a/python/plugins/db_manager/db_plugins/vlayers/connector.py b/python/plugins/db_manager/db_plugins/vlayers/connector.py
index c04503cd8f0..2182cb5ddc2 100644
--- a/python/plugins/db_manager/db_plugins/vlayers/connector.py
+++ b/python/plugins/db_manager/db_plugins/vlayers/connector.py
@@ -96,6 +96,9 @@ class VLayerRegistry(object):
         lid = self.layers.get(l)
         if lid is None:
             return lid
+        if lid not in QgsProject.instance().mapLayers().keys():
+            self.layers.pop(l)
+            return None
         return QgsProject.instance().mapLayer(lid)
 
 
@@ -249,12 +252,16 @@ class VLayerConnector(DBConnector):
     def getTableRowCount(self, table):
         t = table[1]
         l = VLayerRegistry.instance().getLayer(t)
+        if not l or not l.isValid():
+            return None
         return l.featureCount()
 
     def getTableFields(self, table):
         """ return list of columns in table """
         t = table[1]
         l = VLayerRegistry.instance().getLayer(t)
+        if not l or not l.isValid():
+            return []
         # id, name, type, nonnull, default, pk
         n = l.dataProvider().fields().size()
         f = [(i, f.name(), f.typeName(), False, None, False)
@@ -280,6 +287,8 @@ class VLayerConnector(DBConnector):
             l = QgsProject.instance().mapLayer(t)
         else:
             l = VLayerRegistry.instance().getLayer(t)
+        if not l or not l.isValid():
+            return None
         e = l.extent()
         r = (e.xMinimum(), e.yMinimum(), e.xMaximum(), e.yMaximum())
         return r
diff --git a/python/plugins/db_manager/layer_preview.py b/python/plugins/db_manager/layer_preview.py
index ef50bb40f21..dbb35f20b77 100644
--- a/python/plugins/db_manager/layer_preview.py
+++ b/python/plugins/db_manager/layer_preview.py
@@ -113,15 +113,16 @@ class LayerPreview(QgsMapCanvas):
                 else:
                     vl = table.toMapLayer()
 
-                if not vl.isValid():
+                if vl and not vl.isValid():
                     vl.deleteLater()
                     vl = None
 
             # remove old layer (if any) and set new
             if self.currentLayer:
-                QgsProject.instance().removeMapLayers([self.currentLayer.id()])
+                if not QgsProject.instance().layerTreeRoot().findLayer(self.currentLayer.id()):
+                    QgsProject.instance().removeMapLayers([self.currentLayer.id()])
 
-            if vl:
+            if vl and vl.isValid():
                 self.setLayers([vl])
                 QgsProject.instance().addMapLayers([vl], False)
                 self.zoomToFullExtent()