diff --git a/plugins/voxel_layer.cpp b/plugins/voxel_layer.cpp
index 86ddb4a..b7c2177 100755
--- a/plugins/voxel_layer.cpp
+++ b/plugins/voxel_layer.cpp
@@ -102,7 +102,7 @@ bool VoxelLayer::getParams(const std::string& config_file_name, robot::NodeHandl
     if (nh.hasParam("unknown_threshold"))
     {
       nh.getParam("unknown_threshold", unknown_threshold);
-      unknown_threshold_ = unknown_threshold;
+      unknown_threshold_ = unknown_threshold + (VOXEL_BITS - size_z_);
     }
     if (nh.hasParam("mark_threshold"))
     {
@@ -111,9 +111,6 @@ bool VoxelLayer::getParams(const std::string& config_file_name, robot::NodeHandl
     }
     if (nh.hasParam("combination_method"))
       nh.getParam("combination_method", combination_method_);
-
-    
-    
     
 
     this->matchSize();