diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index f1c56c8..93d30d4 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -13,7 +13,7 @@ jobs:
     runs-on: macos-latest
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: [3.6, 3.7, 3.8, 3.9]
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python ${{ matrix.python-version }}
@@ -27,5 +27,5 @@ jobs:
         poetry install
     - name: Run checks
       run: |
-        pre-commit run --all-files
+        pre-commit run --all-files --show-diff-on-failure
         poetry run pytest tests.py --hypothesis-show-statistics --verbose
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index e1c9e64..bbeb173 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -3,6 +3,7 @@ repos:
   rev: stable
   hooks:
   - id: black
+    language_version: python3
 - repo: https://github.com/pre-commit/pre-commit-hooks
   rev: v2.4.0
   hooks:
diff --git a/pyproject.toml b/pyproject.toml
index 9946000..399f1f2 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "pasteboard"
-version = "0.3.1"
+version = "0.3.2"
 description = "Pasteboard - Python interface for reading from NSPasteboard (macOS clipboard)"
 authors = ["Toby Fleming <tobywf@users.noreply.github.com>"]
 license = "MPL-2.0"
@@ -17,6 +17,7 @@ classifiers = [
     "Programming Language :: Python :: 3.6",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: Implementation :: CPython",
     "Topic :: Desktop Environment",
     "Topic :: Software Development :: Libraries",
@@ -28,10 +29,11 @@ build = "build.py"
 python = "^3.6"
 
 [tool.poetry.dev-dependencies]
-black = "^19.10b0"
-pytest = "^5.3.5"
-hypothesis = "^5.5.4"
-mypy = "^0.761"
+black = "^20.8b1"
+pytest = "^6.1.1"
+hypothesis = "^5.37.4"
+mypy = "^0.790"
 
 [build-system]
-requires = ["poetry>=1.0.0"]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
diff --git a/tests.py b/tests.py
index c2c736c..776663a 100644
--- a/tests.py
+++ b/tests.py
@@ -184,7 +184,7 @@ def test_type_hints_get_contents_valid_both_args(tmp_path):
     assert exit_status == 0, normal_report
 
 
-@pytest.mark.parametrize("arg", ['"bar"', 'foo="bar"', 'type="bar"', 'diff="bar"',])
+@pytest.mark.parametrize("arg", ['"bar"', 'foo="bar"', 'type="bar"', 'diff="bar"'])
 def test_type_hints_get_contents_invalid_arg(arg, tmp_path):
     normal_report, error_report, exit_status = mypy_run(
         tmp_path,
@@ -198,7 +198,7 @@ def test_type_hints_get_contents_invalid_arg(arg, tmp_path):
     assert "No overload variant" in normal_report
 
 
-@pytest.mark.parametrize("arg", ['"bar"', 'b"bar"',])
+@pytest.mark.parametrize("arg", ['"bar"', 'b"bar"'])
 def test_type_hints_set_contents_valid_no_args(arg, tmp_path):
     normal_report, error_report, exit_status = mypy_run(
         tmp_path,
@@ -211,7 +211,7 @@ def test_type_hints_set_contents_valid_no_args(arg, tmp_path):
     assert exit_status == 0, normal_report
 
 
-@pytest.mark.parametrize("arg", ['"bar"', 'b"bar"',])
+@pytest.mark.parametrize("arg", ['"bar"', 'b"bar"'])
 def test_type_hints_set_contents_valid_type_args(arg, tmp_path):
     normal_report, error_report, exit_status = mypy_run(
         tmp_path,