diff --git a/CHANGES.rst b/CHANGES.rst
index 320393b..3f2889c 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -5,7 +5,9 @@
 3.0.1 (unreleased)
 ==================
 
-- Nothing changed yet.
+- Fix the ``ExtentFilteredSet`` to only unindex documents that were
+  previously indexed. This avoids an extra ``readCurrent`` call. See
+  `issue 12 <https://github.com/NextThought/nti.zope_catalog/issues/12>`_.
 
 
 3.0.0 (2021-05-12)
diff --git a/src/nti/zope_catalog/tests/test_topic.py b/src/nti/zope_catalog/tests/test_topic.py
index 5ba1d37..7415830 100644
--- a/src/nti/zope_catalog/tests/test_topic.py
+++ b/src/nti/zope_catalog/tests/test_topic.py
@@ -8,13 +8,15 @@
 # stdlib imports
 import unittest
 
+
+from hamcrest import assert_that
+from hamcrest import is_
+
 from zope.index.topic.filter import PythonFilteredSet
 
 from nti.zope_catalog.topic import ExtentFilteredSet
 from nti.zope_catalog.topic import TopicIndex
 
-from hamcrest import assert_that
-from hamcrest import is_
 
 __docformat__ = "restructuredtext en"
 
@@ -123,3 +125,35 @@ def test_ids_and_extent(self):
         extent_extent = extent.getExtent()
         assert_that(list(extent_extent.set),
                     is_([1]))
+
+    def test_index_doc_doesnt_unindex_on_ValueError(self):
+        extent = ExtentFilteredSet('extent', default_expression)
+        in_none = Context(docid=4)
+        extent.unindex_doc = lambda *args: self.fail("Should not call")
+        extent.index_doc(in_none.docid, in_none)
+
+        assert_that(extent.ids(), is_(()))
+
+    def test_index_doc_doesnt_unindex_on_ValueError_with_jar(self):
+        extent = ExtentFilteredSet('extent', default_expression)
+
+
+        in_extent = Context(in_extent=True, docid=1)
+        in_none = Context(docid=4)
+        # The Python implementation of BTrees always calls readCurrent, but
+        # the C implementation doesn't do it if its empty.
+        extent.index_doc(in_extent.docid, in_extent)
+
+        # Now break the jar
+        class MockJar(object):
+            def readCurrent(self, _):
+                raise AssertionError("Should not call") # pragma: no cover
+
+        extent._ids._p_jar = MockJar()
+        extent._ids._p_oid = b'12345678'
+        extent._extent._p_jar = MockJar()
+        extent._extent._p_oid = b'12345678'
+
+        extent.index_doc(in_none.docid, in_none)
+
+        assert_that(extent.ids(), is_((1,)))
diff --git a/src/nti/zope_catalog/topic.py b/src/nti/zope_catalog/topic.py
index f63850d..ce432bc 100644
--- a/src/nti/zope_catalog/topic.py
+++ b/src/nti/zope_catalog/topic.py
@@ -130,7 +130,16 @@ def index_doc(self, docid, context):
         try:
             self._extent.add(docid, context)
         except ValueError:
-            self.unindex_doc(docid)
+            # Only unindex if it was found in the index to start with.
+            # Trying to remove a missing docid still leads to readCurrent()
+            # being called on the underlying BTree set unnecessarily.
+            # This leads to traversing the BTree twice in the uncommon case
+            # of removing an existing object, but that's fine.
+            # (TODO: Can there be persistence errors that break `in` but let
+            # `remove()` keep working?)
+            # See https://github.com/NextThought/nti.zope_catalog/issues/12
+            if docid in self._ids:
+                self.unindex_doc(docid)
 
     def getExtent(self):
         """