diff --git a/dev-requirements.txt b/dev-requirements.txt
index 0b7977f3..756bd6ff 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -1,4 +1,5 @@
 flake8
+flake8-bugbear
 hypothesis
 mypy==0.641
 perf
diff --git a/ppb_vector/vector2.py b/ppb_vector/vector2.py
index 13abbfb1..8b85261e 100644
--- a/ppb_vector/vector2.py
+++ b/ppb_vector/vector2.py
@@ -239,7 +239,7 @@ def angle(self: VectorOrSub, other: VectorLike) -> float:
 
     def isclose(self: VectorOrSub, other: VectorLike, *,
                 abs_tol: Realish = 1e-3, rel_tol: Realish = 1e-06,
-                rel_to: typing.Sequence[VectorLike] = []) -> bool:
+                rel_to: typing.Sequence[VectorLike] = ()) -> bool:
         """
         Determine whether two vectors are close in value.
 
diff --git a/setup.cfg b/setup.cfg
index c8de6df4..39f42289 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,3 +1,4 @@
 [flake8]
+select = E,F,W,B,B9
 ignore = E704
 max-line-length = 100
diff --git a/tests/utils.py b/tests/utils.py
index 092110e8..d37f2ee7 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -4,6 +4,9 @@
 import hypothesis.strategies as st
 
 
+UNIT_X, UNIT_Y = Vector2(1, 0), Vector2(0, 1)
+
+
 def angles():
     return st.floats(min_value=-360, max_value=360)
 
@@ -25,7 +28,7 @@ def vectors(max_magnitude=1e75):
 
 
 def units():
-    return st.builds(Vector2(1, 0).rotate, angles())
+    return st.builds(UNIT_X.rotate, angles())
 
 
 def angle_isclose(x, y, epsilon=6.5e-5):
@@ -39,7 +42,7 @@ def isclose(
     abs_tol: float = 1e-9,
     rel_tol: float = 1e-9,
     rel_exp: float = 1,
-    rel_to: Sequence[Union[float, Vector2]] = [],
+    rel_to: Sequence[Union[float, Vector2]] = (),
 ):
     if rel_exp < 1:
         raise ValueError(f"Expected rel_exp >= 1, got {rel_exp}")
@@ -84,5 +87,5 @@ def isclose(
 
 
 # Sequence of vector-likes equivalent to the input vector (def. to the x vector)
-def vector_likes(v: Vector2 = Vector2(1, 0)):
+def vector_likes(v: Vector2 = UNIT_X):
     return ((v.x, v.y), [v.x, v.y], {"x": v.x, "y": v.y})