diff --git a/pcmdi_metrics/variability_mode/variability_modes_driver.py b/pcmdi_metrics/variability_mode/variability_modes_driver.py
index b2f457c69..e7f3ed769 100755
--- a/pcmdi_metrics/variability_mode/variability_modes_driver.py
+++ b/pcmdi_metrics/variability_mode/variability_modes_driver.py
@@ -540,7 +540,7 @@
 
     model_path_list = sort_human(model_path_list)
 
-    debug_print("model_path_list: " + str(model_path_list), debug)
+    debug_print(f"model_path_list: f{model_path_list}", debug)
 
     # Find where run can be gripped from given filename template for modpath
     if realization == "*":