diff --git a/main.nf b/main.nf
index 304c41d..0dba77c 100644
--- a/main.nf
+++ b/main.nf
@@ -41,7 +41,7 @@ process squirrel {
     if ( params.include_background )
         extra += " --include-background"
     if ( params.additional_background )
-        extra += " --additional-background bg.fa"
+        extra += " -bf bg.fa"
     if ( params.outgroups )
         extra += " --outgroups ${params.outgroups}"