diff --git a/tools/keil.py b/tools/keil.py
index ef0dece3f88122112b28bb1f7fd5a1eac9feb9dc..912c358488495ba8cb0647d58b22d7ebf775d28f 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)