diff --git a/workflow/main.nf b/workflow/main.nf
index 0593d32f3804ecb2b2f46902f26787a5ffce1e68..ecdf62549465d46945c31317bc66dc1e7f96964f 100755
--- a/workflow/main.nf
+++ b/workflow/main.nf
@@ -43,7 +43,7 @@ process tolines {
     file "${uppercase.name}.tolines" into tolines
 
     """
-    cat "$uppercase" | tr -cs "a-z'" "\012"  > "${uppercase.name}.tolines"
+    cat "$uppercase" | tr -cs "A-Z'" "\012"  > "${uppercase.name}.tolines"
     """
 
 }