diff --git a/src/mdevaluate/distribution.py b/src/mdevaluate/distribution.py
index dd069a7..501b71a 100644
--- a/src/mdevaluate/distribution.py
+++ b/src/mdevaluate/distribution.py
@@ -120,7 +120,7 @@ def gr(
 
 
 def distance_distribution(
-    atoms: CoordinateFrame, bins: Optional[int, ArrayLike]
+    atoms: CoordinateFrame, bins: Union[int, ArrayLike]
 ) -> NDArray:
     connection_vectors = atoms[:-1, :] - atoms[1:, :]
     connection_lengths = (connection_vectors**2).sum(axis=1) ** 0.5
diff --git a/src/mdevaluate/pbc.py b/src/mdevaluate/pbc.py
index 16678d8..8755b43 100644
--- a/src/mdevaluate/pbc.py
+++ b/src/mdevaluate/pbc.py
@@ -1,5 +1,6 @@
+from __future__ import annotations
 from collections import OrderedDict
-from typing import Optional, Union
+from typing import Optional, Union, TYPE_CHECKING
 
 import numpy as np
 from numpy.typing import ArrayLike, NDArray
@@ -7,7 +8,8 @@ from numpy.typing import ArrayLike, NDArray
 from itertools import product
 
 from .logging import logger
-from .coordinates import CoordinateFrame
+if TYPE_CHECKING:
+    from mdevaluate.coordinates import CoordinateFrame
 
 
 def pbc_diff(
@@ -70,7 +72,7 @@ def pbc_diff_tric(coords_a: NDArray, coords_b: NDArray, box: NDArray) -> NDArray
 
 
 def pbc_dist(
-    atoms_a: CoordinateFrame, atoms_b: CoordinateFrame, box: Optional[NDArray] = None
+    atoms_a: NDArray, atoms_b: NDArray, box: Optional[NDArray] = None
 ) -> ArrayLike:
     return ((pbc_diff(atoms_a, atoms_b, box) ** 2).sum(axis=1)) ** 0.5