diff --git a/chemfiles/ffi.py b/chemfiles/_c_api.py
similarity index 100%
rename from chemfiles/ffi.py
rename to chemfiles/_c_api.py
diff --git a/chemfiles/clib.py b/chemfiles/_c_lib.py
similarity index 94%
rename from chemfiles/clib.py
rename to chemfiles/_c_lib.py
index afc66719..6d6f9238 100644
--- a/chemfiles/clib.py
+++ b/chemfiles/_c_lib.py
@@ -1,7 +1,7 @@
 # -* coding: utf-8 -*
 import os
 import sys
-from ctypes import cdll, c_double, POINTER
+from ctypes import POINTER, c_double, cdll
 
 try:
     from .external import EXTERNAL_CHEMFILES
@@ -18,8 +18,7 @@ def __call__(self):
             path = _lib_path()
             self._cache = cdll.LoadLibrary(path)
 
-            from .ffi import set_interface
-            from .ffi import CHFL_FRAME, CHFL_ATOM, chfl_vector3d
+            from ._c_api import CHFL_ATOM, CHFL_FRAME, chfl_vector3d, set_interface
 
             set_interface(self._cache)
             # We update the arguments here, as ctypes can not pass a NULL value
@@ -60,8 +59,8 @@ def _lib_path():
 
 
 def _check_dll(path):
-    import struct
     import platform
+    import struct
 
     IMAGE_FILE_MACHINE_I386 = 332
     IMAGE_FILE_MACHINE_AMD64 = 34404
diff --git a/chemfiles/cell.py b/chemfiles/cell.py
index 9afaa454..84682993 100644
--- a/chemfiles/cell.py
+++ b/chemfiles/cell.py
@@ -5,7 +5,7 @@
 import numpy as np
 
 from .utils import CxxPointer, ChemfilesError
-from .ffi import chfl_cellshape, chfl_vector3d
+from ._c_api import chfl_cellshape, chfl_vector3d
 
 
 class CellShape(IntEnum):
diff --git a/chemfiles/frame.py b/chemfiles/frame.py
index 871a3196..a8bbec3d 100644
--- a/chemfiles/frame.py
+++ b/chemfiles/frame.py
@@ -5,7 +5,7 @@
 
 from .utils import CxxPointer, string_type
 from .misc import ChemfilesError
-from .ffi import chfl_vector3d, chfl_bond_order
+from ._c_api import chfl_vector3d, chfl_bond_order
 from .atom import Atom
 from .topology import Topology
 from .cell import UnitCell
diff --git a/chemfiles/misc.py b/chemfiles/misc.py
index 32006846..a48c1111 100644
--- a/chemfiles/misc.py
+++ b/chemfiles/misc.py
@@ -4,7 +4,7 @@
 
 from ctypes import c_uint64, POINTER, create_string_buffer
 
-from .clib import _get_c_library
+from ._c_lib import _get_c_library
 
 
 class ChemfilesWarning(UserWarning):
@@ -128,7 +128,7 @@ def formats_list():
 
     :rtype: list(FormatMetadata)
     """
-    from .ffi import chfl_format_metadata
+    from ._c_api import chfl_format_metadata
 
     lib = _get_c_library()
 
@@ -156,7 +156,7 @@ def set_warnings_callback(function):
 
     By default, warnings are send to python ``warnings`` module.
     """
-    from .ffi import chfl_warning_callback
+    from ._c_api import chfl_warning_callback
 
     def callback(message):
         try:
diff --git a/chemfiles/property.py b/chemfiles/property.py
index 0f3803e6..877d7dea 100644
--- a/chemfiles/property.py
+++ b/chemfiles/property.py
@@ -4,7 +4,7 @@
 import numpy as np
 from ctypes import c_double, c_bool
 
-from .ffi import chfl_property_kind, chfl_vector3d
+from ._c_api import chfl_property_kind, chfl_vector3d
 from .misc import ChemfilesError
 from .utils import CxxPointer, _call_with_growing_buffer, string_type
 
diff --git a/chemfiles/selection.py b/chemfiles/selection.py
index 79047e67..af600b54 100644
--- a/chemfiles/selection.py
+++ b/chemfiles/selection.py
@@ -5,7 +5,7 @@
 import numpy as np
 
 from .utils import CxxPointer, _call_with_growing_buffer
-from .ffi import chfl_match
+from ._c_api import chfl_match
 
 
 class Selection(CxxPointer):
diff --git a/chemfiles/topology.py b/chemfiles/topology.py
index c27fe6af..ac293174 100644
--- a/chemfiles/topology.py
+++ b/chemfiles/topology.py
@@ -5,7 +5,7 @@
 import numpy as np
 
 from .utils import CxxPointer
-from .ffi import chfl_bond_order
+from ._c_api import chfl_bond_order
 from .atom import Atom
 from .residue import Residue
 
diff --git a/chemfiles/utils.py b/chemfiles/utils.py
index 06491d3e..8d94bd17 100644
--- a/chemfiles/utils.py
+++ b/chemfiles/utils.py
@@ -3,7 +3,7 @@
 import sys
 from ctypes import create_string_buffer, c_uint64
 
-from .clib import _get_c_library
+from ._c_lib import _get_c_library
 from .misc import ChemfilesError, _last_error
 
 
diff --git a/tests/misc.py b/tests/misc.py
index 46921716..faf3bc33 100644
--- a/tests/misc.py
+++ b/tests/misc.py
@@ -20,7 +20,7 @@ def __exit__(self, *args):
 
 class TestVersion(unittest.TestCase):
     def test_version(self):
-        version = chemfiles.clib._get_c_library().chfl_version()
+        version = chemfiles._c_lib._get_c_library().chfl_version()
         self.assertEqual(chemfiles.__version__, version.decode("utf8"))