diff --git a/doc/fake__soundfile.py b/doc/fake__soundfile.py
index 22f5061..d5535a8 100644
--- a/doc/fake__soundfile.py
+++ b/doc/fake__soundfile.py
@@ -1,6 +1,7 @@
 """Mock module for Sphinx autodoc."""
 
 import ctypes
+import ctypes.util
 
 # Monkey-patch ctypes to disable searching for libsndfile
 ctypes.util.find_library = lambda _: NotImplemented