diff --git a/tools/keil.py b/tools/keil.py
index f85bb767bf..4cbfb97faf 100644
--- a/tools/keil.py
+++ b/tools/keil.py
@@ -268,7 +268,7 @@ def MDK45Project(tree, target, script):
 
     # write include path, definitions and link flags
     IncludePath = tree.find('Targets/Target/TargetOption/TargetArmAds/Cads/VariousControls/IncludePath')
-    IncludePath.text = ';'.join([_make_path_relative(project_path, os.path.normpath(i)) for i in CPPPATH])
+    IncludePath.text = ';'.join([_make_path_relative(project_path, os.path.normpath(i)) for i in set(CPPPATH)])
 
     Define = tree.find('Targets/Target/TargetOption/TargetArmAds/Cads/VariousControls/Define')
     Define.text = ', '.join(set(CPPDEFINES))