diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 9cbf379..8f898e4 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -233,7 +233,7 @@ jobs:
           python -m coverage run -p -m zope.testrunner --test-path=src --auto-color --auto-progress
       - name: Run tests without C extensions
         run: |
-          PURE_PYTHON=1 AC_PURE_PYTHON=1 python -m coverage run -p -m zope.testrunner --test-path=src --auto-color --auto-progress
+          PURE_PYTHON=1 python -m coverage run -p -m zope.testrunner --test-path=src --auto-color --auto-progress
       - name: Report Coverage
         run: |
           coverage combine
diff --git a/CHANGES.rst b/CHANGES.rst
index f6a7e9e..e481d49 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -8,8 +8,8 @@ For changes before version 3.0, see ``HISTORY.rst``.
 
 - Provide ``AccessControl.get_safe_globals`` to facilitate safe use.
 
-- Use ``AC_PURE_PYTHON`` as switch to enable python implementation as default.
-  This should not be used except for tests and debugging.
+- Honor ``PURE_PYTHON`` environment variable to enable python implementation
+  during runtime.
 
 
 5.2 (2021-07-30)
diff --git a/buildout.cfg b/buildout.cfg
index c257d43..afbc7c2 100644
--- a/buildout.cfg
+++ b/buildout.cfg
@@ -7,8 +7,6 @@ parts = interpreter test coverage
 
 [versions]
 AccessControl =
-RestrictedPython =
-Acquisition = 4.10
 
 [interpreter]
 recipe = zc.recipe.egg
diff --git a/src/AccessControl/Implementation.py b/src/AccessControl/Implementation.py
index 973a082..638a5a0 100644
--- a/src/AccessControl/Implementation.py
+++ b/src/AccessControl/Implementation.py
@@ -29,11 +29,8 @@
 import os
 
 
-# We cannot use `PURE_PYTHON` as this would be propagated to `ExtensionClass`
-# and `Acquisition`. Due to restrictions of python implementation concerning
-# proxies it is not possible to run all with pure python and we influence only
-# the AccessControl implementation here.
-CAPI = not int(os.environ.get('AC_PURE_PYTHON', '0'))
+PURE_PYTHON = int(os.environ.get('PURE_PYTHON', '0'))
+CAPI = not PURE_PYTHON
 
 
 def getImplementationName():
diff --git a/tox.ini b/tox.ini
index 3ea6fcf..8f8fe65 100644
--- a/tox.ini
+++ b/tox.ini
@@ -21,7 +21,6 @@ deps =
 skip_install = true
 setenv =
     PURE_PYTHON=1
-    AC_PURE_PYTHON=1
 
 [testenv:coverage]
 basepython = python3