diff --git a/benchexec/tools/cpachecker.py b/benchexec/tools/cpachecker.py
index f55cca7a3..86d4309fd 100644
--- a/benchexec/tools/cpachecker.py
+++ b/benchexec/tools/cpachecker.py
@@ -194,8 +194,8 @@ def option_present(option):
                 options += [f"{prefix}witness", possible_witness_files[0]]
             else:
                 raise benchexec.tools.template.UnsupportedFeatureException(
-                    f"You are passing a witness as both an option and through the task definition. "
-                    f"Please remove one of them."
+                    "You are passing a witness as both an option and through the task definition. "
+                    "Please remove one of them."
                 )
 
         return options