diff --git a/vctk_preprocess/extract_feats.py b/vctk_preprocess/extract_feats.py
index e344397b..81bd7cf2 100644
--- a/vctk_preprocess/extract_feats.py
+++ b/vctk_preprocess/extract_feats.py
@@ -660,7 +660,7 @@ def format_info_tup(info_tup):
             ex_line_replace = n
             break
 
-    ex_lines[ex_line_replace] = 'merlin_dir="%s"' % merlin_dir
+    ex_lines[ex_line_replace] = f'merlin_dir="{merlin_dir}"'
 
     ex_line_replace = None
     for n, l in enumerate(ex_lines):