diff --git a/BTrees/_base.py b/BTrees/_base.py
index b42ee83..e7dd815 100644
--- a/BTrees/_base.py
+++ b/BTrees/_base.py
@@ -1050,6 +1050,7 @@ def _del(self, key):
                     self._firstbucket = child._next
                     removed_first_bucket = True
             del data[index]
+            self._p_changed = True
 
         return removed_first_bucket, value
 
diff --git a/BTrees/tests/common.py b/BTrees/tests/common.py
index 1267704..1f0e3ad 100644
--- a/BTrees/tests/common.py
+++ b/BTrees/tests/common.py
@@ -91,24 +91,14 @@ class SignedMixin(object):
     KEY_RANDRANGE_ARGS = (-2000, 2001)
 
 
-class Base(SignedMixin):
-    # Tests common to all types: sets, buckets, and BTrees
+class ZODBAccess(object):
 
     db = None
 
-    def _getTargetClass(self):
-        raise NotImplementedError("subclass should return the target type")
-
-    def _makeOne(self):
-        return self._getTargetClass()()
-
-    def setUp(self):
-        super(Base, self).setUp()
-        _skip_if_pure_py_and_py_test(self)
-
     def tearDown(self):
         if self.db is not None:
             self.db.close()
+            del self.db
 
     def _getRoot(self):
         from ZODB import DB
@@ -131,6 +121,21 @@ def _closeRoot(self, root):
         transaction.abort()
         root._p_jar.close()
 
+    
+class Base(ZODBAccess, SignedMixin):
+    # Tests common to all types: sets, buckets, and BTrees
+
+    def _getTargetClass(self):
+        raise NotImplementedError("subclass should return the target type")
+
+    def _makeOne(self):
+        return self._getTargetClass()()
+
+    def setUp(self):
+        super(Base, self).setUp()
+        _skip_if_pure_py_and_py_test(self)
+
+
     def testPersistentSubclass(self):
         # Can we subclass this and Persistent?
         # https://github.com/zopefoundation/BTrees/issues/78
diff --git a/BTrees/tests/testPersistency.py b/BTrees/tests/testPersistency.py
new file mode 100644
index 0000000..4b36554
--- /dev/null
+++ b/BTrees/tests/testPersistency.py
@@ -0,0 +1,47 @@
+##############################################################################
+#
+# Copyright (c) 2020 Zope Foundation and Contributors.
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE
+#
+##############################################################################
+
+from unittest import TestCase
+
+from ..OOBTree import OOBTree, OOBTreePy
+from .common import _skip_wo_ZODB, ZODBAccess
+
+
+BUCKET_SIZE = OOBTreePy.max_leaf_size
+
+
+class TestPersistency(ZODBAccess, TestCase):
+    @_skip_wo_ZODB
+    def test_empty_bucket_persistency(self):
+        from transaction import commit
+        root = self._getRoot()
+        try:
+            # tree with 3 buckets (internal implementation details)
+            tree = OOBTree(
+                dict((i, i) for i in range(3 * BUCKET_SIZE // 2 + 2)))
+            root["tree"] = tree
+            commit()
+            # almost clear the second bucket keeping the last element
+            for i in range(BUCKET_SIZE // 2, BUCKET_SIZE - 1):
+                del tree[i]
+            commit()
+            del tree[BUCKET_SIZE - 1]  # remove the last element
+            commit()
+            tree._check()
+            tree._p_deactivate()
+            tree._check()  # fails in case of bad persistency
+        finally:
+            self._closeRoot(root)
+
+            
diff --git a/CHANGES.rst b/CHANGES.rst
index b2d1d31..c881835 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,6 +5,9 @@
 4.7.3 (unreleased)
 ==================
 
+- Fix persistency bug in the Python version
+  (`#118 <https://github.com/zopefoundation/BTrees/issues/118>`_).
+
 - Fix ``Tree.__setstate__`` to no longer accept children besides
   tree or bucket types to prevent crashes. See `PR 143
   <https://github.com/zopefoundation/BTrees/pull/143>`_ for details.
diff --git a/tox.ini b/tox.ini
index e4cf67a..72890d2 100644
--- a/tox.ini
+++ b/tox.ini
@@ -3,7 +3,7 @@ envlist =
 # Jython support pending 2.7 support, due 2012-07-15 or so.  See:
 # http://fwierzbicki.blogspot.com/2012/03/adconion-to-fund-jython-27.html
 #   py27,jython,pypy,coverage,docs
-    py27,py27-pure,py35,py35-pure,py36,py37,py38,pypy,pypy3,w_zodb,coverage,docs
+    py27,py27-pure,py35,py35-pure,py36,py37,py38,pypy,pypy3,w_zodb,w_zodb-pure,coverage,docs
 
 [testenv]
 usedevelop = true
@@ -29,6 +29,12 @@ basepython =
 deps =
     ZODB
 
+[testenv:w_zodb-pure]
+basepython =
+    python2.7
+deps =
+    ZODB
+
 [testenv:coverage]
 basepython =
     python3.6