diff --git a/vcf2loc.py b/vcf2loc.py
index 26a7d0a..706b4ab 100755
--- a/vcf2loc.py
+++ b/vcf2loc.py
@@ -109,11 +109,14 @@
             # Keeping only SNV sites.
             continue
         if args.min_dp is not None:
+            parent_b_dp = (
+                0 if args.parent_b is None
+                else site.genotype_calls[args.parent_a]['DP']
+            )
             child_dp = (
                 site.depth
                 - site.genotype_calls[args.parent_a]['DP']
-                - 0 if args.parent_b is None
-                  else site.genotype_calls[args.parent_a]['DP']
+                - parent_b_dp
             )
             if child_dp < args.min_dp:
                 # Skipping sites with low depth.