diff --git a/edalize/edatool.py b/edalize/edatool.py
index 85868c79a..848c96961 100644
--- a/edalize/edatool.py
+++ b/edalize/edatool.py
@@ -107,7 +107,7 @@ def check_args(self, unknown):
         # this function to provide custom args checking logic.
 
         if unknown:
-            raise Exception(f'Unknown command line option {unknown[0]}')
+            raise Exception('Unknown command line option',unknown[0])
 
     def configure(self, args):
         logger.info("Setting up project")