diff --git a/pkg/obiformats/ngsfilter_read.go b/pkg/obiformats/ngsfilter_read.go
index 2ace74d..f6dfd37 100644
--- a/pkg/obiformats/ngsfilter_read.go
+++ b/pkg/obiformats/ngsfilter_read.go
@@ -54,8 +54,8 @@ func _parseMainNGSFilterTags(text string) obingslibrary.TagPair {
 	}
 
 	return obingslibrary.TagPair{
-		Forward: tags[0],
-		Reverse: tags[1],
+		Forward: strings.ToLower(tags[0]),
+		Reverse: strings.ToLower(tags[1]),
 	}
 }
 
diff --git a/pkg/obingslibrary/match.go b/pkg/obingslibrary/match.go
index 54cf94a..d188308 100644
--- a/pkg/obingslibrary/match.go
+++ b/pkg/obingslibrary/match.go
@@ -3,9 +3,10 @@ package obingslibrary
 import (
 	"errors"
 	"fmt"
-	log "github.com/sirupsen/logrus"
 	"strings"
 
+	log "github.com/sirupsen/logrus"
+
 	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiapat"
 	"git.metabarcoding.org/lecasofts/go/obitools/pkg/obiseq"
 )
@@ -110,7 +111,7 @@ func (marker *Marker) Match(sequence *obiseq.BioSequence) *DemultiplexMatch {
 	if len(match) > 0 {
 		sseq := sequence.String()
 		direct := sseq[match[0][0]:match[0][1]]
-		ftag := sseq[(match[0][0] - marker.taglength):match[0][0]]
+		ftag := strings.ToLower(sseq[(match[0][0] - marker.taglength):match[0][0]])
 
 		m := DemultiplexMatch{
 			ForwardMatch:      direct,
@@ -193,7 +194,7 @@ func (marker *Marker) Match(sequence *obiseq.BioSequence) *DemultiplexMatch {
 
 			} else {
 				ftag = ftag.ReverseComplement(true)
-				sftag = ftag.String()
+				sftag = strings.ToLower(ftag.String())
 			}
 
 			m.ForwardMatch = direct.String()