diff --git a/sequence_extractor/exon_concatenation.py b/sequence_extractor/exon_concatenation.py
index 666c303a5007b95492fcb050e05fd40d81ec7be0..d95ef0ac629adb5b3c66078f3877bd8eb22f518e 100644
--- a/sequence_extractor/exon_concatenation.py
+++ b/sequence_extractor/exon_concatenation.py
@@ -20,10 +20,8 @@ def exon_concatenation(
                 if annotation[-1] == line1[0:16]:
                     read += line2[:-1]
                 elif annotation[-1] != line1[0:16]:
-                    fasta_format_list.append(annotation[-1])
-                    fasta_format_list.append(read)
+                    fasta_format_list.append((annotation[-1],read))
                     annotation.append(line1[0:16])
                     read = line2[:-1]
-        fasta_format_list.append(annotation[-1])
-        fasta_format_list.append(read)
+        fasta_format_list.append((annotation[-1],read))
     return fasta_format_list