diff --git a/tools/keil.py b/tools/keil.py
index ef0dece3f8..912c358488 100644
--- a/tools/keil.py
+++ b/tools/keil.py
@@ -107,6 +107,7 @@ def MDK4Project(target, script):
     groups = tree.find('Targets/Target/Groups')
     if groups is None:
         groups = SubElement(tree.find('Targets/Target'), 'Groups')
+    groups.clear() # clean old groups
     for group in script:
         group_xml = MDK4AddGroup(ProjectFiles, groups, group['name'], group['src'], project_path)