diff --git a/.travis.yml b/.travis.yml
index 91b611a..42df128 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,7 +2,7 @@ cache: false
 
 _tox: &tox
   install:
-    - pip3 install tox
+    - pip3 install tox tox-travis
   script:
     - tox
 
@@ -17,6 +17,11 @@ jobs:
       script:
         - cd editors/emacs && emacs -batch -l ert -l gersemi.el -l gersemi-tests.el -f ert-run-tests-batch-and-exit
 
+    - language: python
+      os: linux
+      python: "3.6"
+      <<: *tox
+
     - language: python
       os: linux
       python: "3.7"
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1af70b2..73139fd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,16 @@
 # Changelog
 
+## [0.5.0] 2020-08-25
+
+### Added
+- minor performance improvements
+- support for Python 3.6
+
+### Changed
+- files are taken as input only once even if provided multiple times
+- files are no longer overwritten if reformatting wouldn't lead to change of content
+- dependency to `packaging`
+
 ## [0.4.0] 2020-08-05
 
 ### Added
diff --git a/gersemi/__version__.py b/gersemi/__version__.py
index 8895fd1..9946b73 100644
--- a/gersemi/__version__.py
+++ b/gersemi/__version__.py
@@ -4,4 +4,4 @@
 __license__ = "MPL 2.0"
 __title__ = "gersemi"
 __url__ = "https://github.com/BlankSpruce/gersemi"
-__version__ = "0.4.0"
+__version__ = "0.5.0"
diff --git a/setup.py b/setup.py
index 9c9cac0..392d9ba 100644
--- a/setup.py
+++ b/setup.py
@@ -22,9 +22,9 @@
     url=about["__url__"],
     packages=find_packages(include=["gersemi", "gersemi.*"]),
     package_data={"gersemi": ["cmake.lark", "builtin_commands"]},
-    install_requires=["lark-parser>=0.8,<0.10", "pyyaml>=5,<6"],
+    install_requires=["dataclasses", "lark-parser>=0.8,<0.10", "pyyaml>=5,<6"],
     extras_requires=["colorama>=0.4"],
-    python_requires=">=3.7",
+    python_requires=">=3.6",
     entry_points={"console_scripts": ["gersemi = gersemi.__main__:main"]},
     license=about["__license__"],
     classifiers=[
diff --git a/tests/test_executable.py b/tests/test_executable.py
index fd6be0d..768d335 100644
--- a/tests/test_executable.py
+++ b/tests/test_executable.py
@@ -13,6 +13,9 @@ def gersemi(*gersemi_args, **subprocess_kwargs):
     return subprocess.run(
         [sys.executable, "-m", "gersemi", *gersemi_args],
         check=False,
+        encoding="utf8",
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
         **subprocess_kwargs,
     )
 
@@ -161,18 +164,18 @@ def test_format_file_in_place():
 def test_check_formatted_input_from_stdin():
     inp = """set(FOO BAR)
 """
-    assert_success("--check", "-", input=inp, text=True)
+    assert_success("--check", "-", input=inp)
 
 
 def test_check_not_formatted_input_from_stdin():
     inp = """set(FOO BAR)"""  # missing newline at the end
-    assert_fail("--check", "-", input=inp, text=True)
+    assert_fail("--check", "-", input=inp)
 
 
 def test_format_formatted_input_from_stdin():
     inp = """set(FOO BAR)
 """
-    completed_process = gersemi("-", input=inp, text=True, capture_output=True)
+    completed_process = gersemi("-", input=inp)
     assert completed_process.returncode == 0
     assert completed_process.stdout == inp
     assert completed_process.stderr == ""
@@ -181,7 +184,7 @@ def test_format_formatted_input_from_stdin():
 def test_format_not_formatted_input_from_stdin():
     inp = "set(FOO BAR)"  # missing newline at the end
 
-    completed_process = gersemi("-", input=inp, text=True, capture_output=True)
+    completed_process = gersemi("-", input=inp)
     assert completed_process.returncode == 0
     assert completed_process.stdout == inp + "\n"
     assert completed_process.stderr == ""
@@ -302,7 +305,7 @@ def test_format_with_default_line_length():
     inp = "set(FOO long_argument__________________________________________________________)"
     outp = inp + "\n"
     assert len(inp) == 80
-    completed_process = gersemi("-", input=inp + "\n", text=True, capture_output=True)
+    completed_process = gersemi("-", input=inp + "\n")
     assert completed_process.returncode == 0
     assert completed_process.stdout == outp
     assert completed_process.stderr == ""
@@ -313,7 +316,7 @@ def test_format_with_default_line_length():
 )
 """
     assert len(inp2) > 80
-    completed_process = gersemi("-", input=inp2 + "\n", text=True, capture_output=True)
+    completed_process = gersemi("-", input=inp2 + "\n")
     assert completed_process.returncode == 0
     assert completed_process.stdout == outp2
     assert completed_process.stderr == ""
@@ -329,8 +332,7 @@ def test_format_with_non_default_line_length():
         str(line_length),
         "-",
         input=inp + "\n",
-        text=True,
-        capture_output=True,
+        universal_newlines=True,
     )
     assert completed_process.returncode == 0
     assert completed_process.stdout == outp
@@ -347,8 +349,7 @@ def test_format_with_non_default_line_length():
         str(line_length),
         "-",
         input=inp2 + "\n",
-        text=True,
-        capture_output=True,
+        universal_newlines=True,
     )
     assert completed_process.returncode == 0
     assert completed_process.stdout == outp2
@@ -400,9 +401,7 @@ def test_format_project_with_custom_commands_but_without_definitions():
 
 
 def test_non_empty_stderr_when_files_are_not_formatted():
-    completed_process = gersemi(
-        "--check", case("custom_project/not_formatted"), text=True, capture_output=True,
-    )
+    completed_process = gersemi("--check", case("custom_project/not_formatted"))
     assert completed_process.returncode == 1
     assert completed_process.stderr != ""
 
@@ -412,8 +411,7 @@ def test_empty_stderr_when_files_are_not_formatted_but_quiet_is_supplied():
         "--check",
         case("custom_project/not_formatted"),
         "--quiet",
-        text=True,
-        capture_output=True,
+        universal_newlines=True,
     )
     assert completed_process.returncode == 1
     assert completed_process.stderr == ""
@@ -594,9 +592,7 @@ def test_use_configuration_file_from_current_directory_when_input_is_from_stdin(
     assert len(inp) > line_length
 
     with create_dot_gersemirc(where=".", line_length=30):
-        completed_process = gersemi(
-            "-", input=inp + "\n", text=True, capture_output=True,
-        )
+        completed_process = gersemi("-", input=inp + "\n")
         assert completed_process.returncode == 0
         assert completed_process.stdout == outp
         assert completed_process.stderr == ""
diff --git a/tox.ini b/tox.ini
index 85bfceb..4c47236 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,14 @@
 [tox]
-envlist = tests, lint, format, mypy
+envlist = py36, py37, py38, lint, format, mypy
+skip_missing_interpreters=true
 
-[testenv:tests]
+[travis]
+python =
+    3.6: py36
+    3.7: py37
+    3.8: py38, lint, format, mypy
+
+[testenv]
 deps =
     pytest
     pytest-clarity
@@ -9,6 +16,8 @@ deps =
 commands =
     pytest {posargs:-n auto}
 
+[testenv:tests]
+
 [testenv:lint]
 deps =
     pylint