diff --git a/CHANGELOG.md b/CHANGELOG.md
index 276cbca5..617d6156 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ CHANGELOG for FlatCAM beta
 - fixed the on_delete() method in the App class; sometime it will delete all files that have similar names
 - made sure that on creation of new objects the adding of the names to the auto-complete list is done properly
 - Drilling Tool - remade the 'Beginner/Advanced' Mode
+- Milling Tool - fixed the ever-growing list of preproessors
 
 8.12.2020
 
diff --git a/appTools/ToolMilling.py b/appTools/ToolMilling.py
index b1bd251c..5b2a5f84 100644
--- a/appTools/ToolMilling.py
+++ b/appTools/ToolMilling.py
@@ -334,6 +334,8 @@ class ToolMilling(AppTool, Excellon):
             "tools_mill_area_overz": self.ui.over_z_entry,
         })
 
+        # reset the Geometry preprocessor combo
+        self.ui.pp_geo_name_cb.clear()
         # populate Geometry (milling) preprocessor combobox list
         for name in list(self.app.preprocessors.keys()):
             self.ui.pp_geo_name_cb.addItem(name)