diff --git a/setup.py b/setup.py
index 09bbbbe..4c917f7 100644
--- a/setup.py
+++ b/setup.py
@@ -6,7 +6,7 @@
 
 setup(
     name="snapgene_reader",
-    version="0.1.18",
+    version="0.1.19",
     author="yishaluo",
     maintainer="EdinburghGenomeFoundry",
     description="Convert Snapgene *.dna files dict/json/biopython.",
diff --git a/snapgene_reader/snapgene_reader.py b/snapgene_reader/snapgene_reader.py
index 71f8b5c..ce32ac1 100644
--- a/snapgene_reader/snapgene_reader.py
+++ b/snapgene_reader/snapgene_reader.py
@@ -12,6 +12,8 @@
 try:
     # Biopython <1.78
     from Bio.Alphabet import DNAAlphabet
+
+    has_dna_alphabet = True
 except ImportError:
     # Biopython >=1.78
     has_dna_alphabet = False