diff --git a/tests/test_bgenwriter.py b/tests/test_bgenwriter.py
index fef1097..1f4bc58 100644
--- a/tests/test_bgenwriter.py
+++ b/tests/test_bgenwriter.py
@@ -322,6 +322,7 @@ def test_phased_data_different_sizes(self):
             for x in bfile:
                 probs = x.probabilities
                 self.assertTrue(probs_close(geno[:, :-1], probs[:, :-1], bit_depth=8))
+            bfile.close()
     
     def test_ploidy_unphased(self):
         ''' check we can write unphased variants with variable ploidy per sample