diff --git a/js/control/Control.Layers.js b/js/control/Control.Layers.js
index bcff8f0..5a92547 100644
--- a/js/control/Control.Layers.js
+++ b/js/control/Control.Layers.js
@@ -79,6 +79,21 @@ BR.ControlLayers = L.Control.Layers.extend({
         var obj = baseLayers[index];
 
         this.activateLayer(obj.layer);
+    },
+
+    _addLayer: function (layer, name, overlay) {
+        L.Control.Layers.prototype._addLayer.call(this, layer, name, overlay);
+
+        // override z-index assignment to fix that base layers added later
+        // are on top of overlays; set all base layers to 0
+		if (this.options.autoZIndex && layer.setZIndex) {
+            if (!overlay) {
+                // undo increase in super method
+                this._lastZIndex--;
+
+                layer.setZIndex(0);
+            }
+		}
     }
 
 });
\ No newline at end of file
diff --git a/js/control/LayersTab.js b/js/control/LayersTab.js
index 1798035..560cc96 100644
--- a/js/control/LayersTab.js
+++ b/js/control/LayersTab.js
@@ -289,7 +289,11 @@ BR.LayersTab = BR.ControlLayers.extend({
 
     createLayer: function (layerData) {
         var layer = this.layersConfig.createLayer(layerData);
-        layer.options.zIndex = this._lastZIndex + 1;
+        var overlay = layerData.properties.overlay;
+
+        // preview z-index, like in BR.ControlLayers._addLayer
+        layer.options.zIndex = overlay ? this._lastZIndex + 1 : 0;
+
         return layer;
     },