diff --git a/physlr/physlr.py b/physlr/physlr.py
index 9c966a1f..a5a6bb35 100644
--- a/physlr/physlr.py
+++ b/physlr/physlr.py
@@ -2694,6 +2694,7 @@ def physlr_find_ntcard_mode(self):
         # Assumption: There is no negative slope to the right of the first local minimum
         freq_count = [int(line.rstrip().split("\t")[2]) for line in open(self.args.FILES[0])
                       if line[0] != "k"]
+        min_idx = 0
         min_val = freq_count[0]
         for idx, freq in enumerate(freq_count):
             if freq > min_val: