diff --git a/coverage/fullcoverage/encodings.py b/coverage/fullcoverage/encodings.py
index b88418663..73bd5646e 100644
--- a/coverage/fullcoverage/encodings.py
+++ b/coverage/fullcoverage/encodings.py
@@ -14,6 +14,9 @@
 a problem with coverage.py - that it starts too late to trace the coverage of
 many of the most fundamental modules in the Standard Library.
 
+DO NOT import other modules into here, it will interfere with the goal of this
+code executing before all imports.  This is why this file isn't type-checked.
+
 """
 
 import sys
diff --git a/pyproject.toml b/pyproject.toml
index d2d2100f5..561ff9f77 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -23,3 +23,7 @@ warn_return_any = true
 warn_unreachable = true
 warn_unused_configs = true
 warn_unused_ignores = true
+
+exclude = """(?x)(
+    ^coverage/fullcoverage/encodings\\.py$      # can't import things into it.
+    )"""
diff --git a/tox.ini b/tox.ini
index ecece7ff5..5a5bfc90d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -102,6 +102,7 @@ setenv =
     C5=coverage/parser.py coverage/phystokens.py coverage/plugin.py coverage/plugin_support.py coverage/python.py
     C6=coverage/report.py coverage/results.py coverage/sqldata.py coverage/summary.py
     C7=coverage/templite.py coverage/tomlconfig.py coverage/types.py coverage/version.py coverage/xmlreport.py
+    # not done yet: html.py pytracer.py
     TYPEABLE_C={env:C1} {env:C2} {env:C3} {env:C4} {env:C5} {env:C6} {env:C7}
     T1=tests/conftest.py tests/coveragetest.py tests/goldtest.py tests/helpers.py tests/mixins.py tests/osinfo.py
     T2=tests/test_annotate.py tests/test_api.py tests/test_arcs.py tests/test_cmdline.py tests/test_collector.py tests/test_concurrency.py