diff --git a/droplets/emulsions.py b/droplets/emulsions.py
index 5818946..af73b3c 100644
--- a/droplets/emulsions.py
+++ b/droplets/emulsions.py
@@ -285,7 +285,7 @@ def data(self) -> np.ndarray:
             if len(classes) > 1:
                 raise TypeError(
                     "Emulsion data cannot be stored contiguously if it contains a "
-                    f"multiple of droplet classes: "
+                    "multiple of droplet classes: "
                     + ", ".join(c.__name__ for c in classes)
                 )
             result = np.array([d.data for d in self])
diff --git a/droplets/tools/spherical.py b/droplets/tools/spherical.py
index 70b9910..e2b650e 100644
--- a/droplets/tools/spherical.py
+++ b/droplets/tools/spherical.py
@@ -199,7 +199,7 @@ def make_volume_from_radius_nd_compiled() -> Callable[[TNumArr, int], TNumArr]:
     """
 
     @register_jitable
-    def volume_from_radius(radius: TNumArr, dim: int) -> TNumArr:
+    def volume_from_radius_impl(radius: TNumArr, dim: int) -> TNumArr:
         if dim == 1:
             return 2 * radius
         elif dim == 2:
@@ -208,7 +208,7 @@ def volume_from_radius(radius: TNumArr, dim: int) -> TNumArr:
             return 4 * π / 3 * radius**3
         raise NotImplementedError
 
-    return volume_from_radius  # type: ignore
+    return volume_from_radius_impl  # type: ignore
 
 
 def surface_from_radius(radius: TNumArr, dim: int) -> TNumArr:
diff --git a/pyproject.toml b/pyproject.toml
index fb82667..a1ce511 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -72,6 +72,7 @@ select = [
     "I",  # isort
     "A",  # flake8-builtins 
     "B",  # flake8-bugbear
+    "F",  # pyflakes
     "C4",  # flake8-comprehensions
     "FA", # flake8-future-annotations
     "ISC", # flake8-implicit-str-concat
@@ -86,7 +87,7 @@ select = [
     "SIM", # flake8-simplify
     "PTH", # flake8-use-pathlib
 ]
-ignore = ["B007", "B027", "B028", "SIM108", "ISC001", "PT006", "PT011", "RET504", "RET505", "RET506"]
+ignore = ["B007", "B027", "B028", "F401", "F403", "SIM108", "ISC001", "PT006", "PT011", "RET504", "RET505", "RET506"]
 
 [tool.ruff.lint.isort]
 section-order = ["future", "standard-library", "third-party", "first-party", "my-modules", "self", "local-folder"]
diff --git a/scripts/format_code.sh b/scripts/format_code.sh
index 8608a54..c183843 100755
--- a/scripts/format_code.sh
+++ b/scripts/format_code.sh
@@ -1,16 +1,11 @@
 #!/usr/bin/env bash
 # This script formats the code of this package
 
-echo "Upgrading python syntax..."
-pushd .. > /dev/null
-find . -name '*.py' -exec pyupgrade --py39-plus {} +
-popd > /dev/null
-
-echo "Formating import statements..."
+echo "Formatting import statements..."
 ruff check --fix --config=../pyproject.toml ..
 
-echo "Formating docstrings..."
+echo "Formatting docstrings..."
 docformatter --in-place --black --recursive ..
 
-echo "Formating source code..."
+echo "Formatting source code..."
 ruff format --config=../pyproject.toml ..
\ No newline at end of file
diff --git a/tests/requirements.txt b/tests/requirements.txt
index eee7d9c..516cba4 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,6 +1,5 @@
 -r ../requirements.txt
 docformatter>=1.7
-pyupgrade>=3
 pytest>=5.4
 pytest-cov>=2.8
 pytest-xdist>=1.30
diff --git a/tests/test_image_analysis.py b/tests/test_image_analysis.py
index 15a085a..b358206 100644
--- a/tests/test_image_analysis.py
+++ b/tests/test_image_analysis.py
@@ -99,7 +99,7 @@ def test_localization_perturbed_2d(periodic, rng):
     assert len(emulsion) == 1
     d2 = emulsion[0]
 
-    msg = "size=%d, periodic=%s, %s != %s" % (size, periodic, d1, d2)
+    msg = f"{size=}, {periodic=}, {d1} != {d2}"
     np.testing.assert_almost_equal(d1.position, d2.position, decimal=1, err_msg=msg)
     assert d1.radius == pytest.approx(d2.radius, rel=1e-5)
     assert d1.interface_width == pytest.approx(d2.interface_width, rel=1e-3)
@@ -129,7 +129,7 @@ def test_localization_perturbed_3d(periodic, rng):
     assert len(emulsion) == 1
     d2 = emulsion[0]
 
-    msg = "size=%d, periodic=%s, %s != %s" % (size, periodic, d1, d2)
+    msg = f"{size=}, {periodic=}, {d1} != {d2}"
     np.testing.assert_almost_equal(d1.position, d2.position, decimal=1, err_msg=msg)
     assert d1.radius == pytest.approx(d2.radius, rel=1e-4)
     assert d1.interface_width == pytest.approx(d2.interface_width, rel=1e-3)