diff --git a/docs/src/en/mutate.md b/docs/src/en/mutate.md
index ac3e25ca..96ac8dad 100644
--- a/docs/src/en/mutate.md
+++ b/docs/src/en/mutate.md
@@ -41,7 +41,7 @@ For use from the terminal (bash): Enclose individual mutation annotations in quo
 
 **Optional arguments**  
 `-k` `--k`  
-Length of sequences flanking the mutation. Default: 31.  
+Length of sequences flanking the mutation. Default: 30.  
 If k > total length of the sequence, the entire sequence will be kept.  
 
 `-mc` `--mut_column`