diff --git a/docs/source/conf.py b/docs/source/conf.py
index 5037c04b1..ac018b71c 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -20,14 +20,19 @@
 # silently goes back to emitting unresolvable annotations.
 from sphinx_autodoc_typehints._resolver import resolve_type_guarded_imports
 
+# NB: this must precede ``import pcapkit``. ``pcapkit.utilities.logging`` reads
+# ``PCAPKIT_SPHINX`` at *import* time to compute ``SPHINX_TYPE_CHECKING``, and
+# importing ``pcapkit`` already pulls in the schema modules -- so setting it any
+# later leaves every ``if SPHINX_TYPE_CHECKING:`` TypedDict undefined and autodoc
+# cannot document them.
+os.environ['PCAPKIT_SPHINX'] = '1'
+
 import pcapkit
 
 if TYPE_CHECKING:
     from typing import Any, Dict, List, Optional
     from sphinx.application import Sphinx
 
-os.environ['PCAPKIT_SPHINX'] = '1'
-
 logger = logging.getLogger('pcapkit-sphinx')
 logger.setLevel(logging.INFO)