diff --git a/dataframe-core.cabal b/dataframe-core.cabal
--- a/dataframe-core.cabal
+++ b/dataframe-core.cabal
@@ -1,6 +1,6 @@
 cabal-version:      3.4
 name:               dataframe-core
-version:            2.5.0.0
+version:            2.5.0.1
 synopsis:           Core data structures for the dataframe library.
 description:
     Minimal interchange-format types for the @dataframe@ ecosystem:
diff --git a/src-internal/DataFrame/Internal/Column.hs b/src-internal/DataFrame/Internal/Column.hs
--- a/src-internal/DataFrame/Internal/Column.hs
+++ b/src-internal/DataFrame/Internal/Column.hs
@@ -4,6 +4,7 @@
 
 * "DataFrame.Internal.Column.Types" — type-level machinery ('Rep', 'SBool', ...)
 * "DataFrame.Internal.Column.Base" — the 'Column' GADT and core definitions
+* "DataFrame.Internal.Column.Bitmap" — the validity bitmap and its helpers
 * "DataFrame.Internal.Column.Properties" — predicates and introspection
 * "DataFrame.Internal.Column.Conversion" — vector\/list conversions
 * "DataFrame.Internal.Column.Operations" — bulk transformations
@@ -13,6 +14,7 @@
 -}
 module DataFrame.Internal.Column (
     module DataFrame.Internal.Column.Base,
+    module DataFrame.Internal.Column.Bitmap,
     module DataFrame.Internal.Column.Conversion,
     module DataFrame.Internal.Column.Operations,
     module DataFrame.Internal.Column.Properties,
@@ -20,6 +22,7 @@
 ) where
 
 import DataFrame.Internal.Column.Base
+import DataFrame.Internal.Column.Bitmap
 import DataFrame.Internal.Column.Conversion
 import DataFrame.Internal.Column.Operations
 import DataFrame.Internal.Column.Properties