diff --git a/tests/test_core.py b/tests/test_core.py
index 6643e08142d9da22cb51a26d7446c7a1b78ca01b..90f8c90b5cfc2f06a32136a8980109b1ddd4f0ad 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -80,7 +80,7 @@ def test_output_results(capsys, tmpdir):
     fmt = "csv"
     quiet = False
     verbose = 0
-    core.output_results(output_file, all_seq_digested, fmt, quiet, verbose)
+    core.output_results(str(output_file), all_seq_digested, fmt, quiet, verbose)
     out, err = capsys.readouterr()
     assert out == output_file.read()
     assert output_file.read() == "Original_header,No_peptide,Enzyme,Cleaving_"\
@@ -97,7 +97,7 @@ def test_output_results(capsys, tmpdir):
     fmt = "tsv"
     quiet = False
     verbose = 0
-    core.output_results(output_file, all_seq_digested, fmt, quiet, verbose)
+    core.output_results(str(output_file), all_seq_digested, fmt, quiet, verbose)
     out, err = capsys.readouterr()
     assert out == output_file.read()
     assert output_file.read() == "Original_header\tNo_peptide\tEnzyme\tCleavi"\
@@ -115,7 +115,7 @@ def test_output_results(capsys, tmpdir):
     fmt = "fasta"
     quiet = False
     verbose = 0
-    core.output_results(output_file, all_seq_digested, fmt, quiet, verbose)
+    core.output_results(str(output_file), all_seq_digested, fmt, quiet, verbose)
     out, err = capsys.readouterr()
     assert out == output_file.read()
     assert output_file.read() == ">Input_0_fake_enzyme1_4_4_534.52598_3.6\nWQ"\
@@ -132,7 +132,7 @@ def test_output_results(capsys, tmpdir):
     fmt = "csv"
     quiet = True
     verbose = 0
-    core.output_results(output_file, all_seq_digested, fmt, quiet, verbose)
+    core.output_results(str(output_file), all_seq_digested, fmt, quiet, verbose)
     out, err = capsys.readouterr()
     # Quiet
     assert out == ""
@@ -152,7 +152,7 @@ def test_output_results(capsys, tmpdir):
     fmt = "csv"
     quiet = False
     verbose = 3
-    core.output_results(output_file, all_seq_digested, fmt, quiet, verbose)
+    core.output_results(str(output_file), all_seq_digested, fmt, quiet, verbose)
     out, err = capsys.readouterr()
     assert output_file.read() == "Original_header,No_peptide,Enzyme,Cleaving_"\
                                  "pos,Peptide_size,Peptide_mass,pI,Sequence\n"\