diff --git a/segmentation_quality_measures/information_theoretic_based_metrics.py b/segmentation_quality_measures/information_theoretic_based_metrics.py
index 2e02ba937d9d51df4e0aead087b3779256682fde..ea94c36564565c174ea90b67e7724e2a99e74fb0 100644
--- a/segmentation_quality_measures/information_theoretic_based_metrics.py
+++ b/segmentation_quality_measures/information_theoretic_based_metrics.py
@@ -325,7 +325,7 @@ def variation_of_information(
 
     if labels is not None:
         raise NotImplementedError(
-            f"Reduction to certain labels is not implemented yet.")
+            "Reduction to certain labels is not implemented yet.")
         # output = torch.index_select(output, dim=1, index=labels)
         # target = torch.index_select(target, dim=1, index=labels)