diff --git a/contrib/import-checker.py b/contrib/import-checker.py
--- a/contrib/import-checker.py
+++ b/contrib/import-checker.py
@@ -31,6 +31,7 @@ allowsymbolimports = (
     'mercurial.node',
     # for revlog to re-export constant to extensions
     'mercurial.revlogutils.constants',
+    'mercurial.revlogutils.flagutil',
     # for cffi modules to re-export pure functions
     'mercurial.pure.base85',
     'mercurial.pure.bdiff',
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -38,13 +38,6 @@ from .i18n import _
 from .revlogutils.constants import (
     FLAG_GENERALDELTA,
     FLAG_INLINE_DATA,
-    REVIDX_DEFAULT_FLAGS,
-    REVIDX_ELLIPSIS,
-    REVIDX_EXTSTORED,
-    REVIDX_FLAGS_ORDER,
-    REVIDX_ISCENSORED,
-    REVIDX_KNOWN_FLAGS,
-    REVIDX_RAWTEXT_CHANGING_FLAGS,
     REVLOGV0,
     REVLOGV1,
     REVLOGV1_FLAGS,
@@ -54,6 +47,15 @@ from .revlogutils.constants import (
     REVLOG_DEFAULT_FORMAT,
     REVLOG_DEFAULT_VERSION,
 )
+from .revlogutils.flagutil import (
+    REVIDX_DEFAULT_FLAGS,
+    REVIDX_ELLIPSIS,
+    REVIDX_EXTSTORED,
+    REVIDX_FLAGS_ORDER,
+    REVIDX_ISCENSORED,
+    REVIDX_KNOWN_FLAGS,
+    REVIDX_RAWTEXT_CHANGING_FLAGS,
+)
 from .thirdparty import (
     attr,
 )
diff --git a/mercurial/revlogutils/flagutil.py b/mercurial/revlogutils/flagutil.py
new file mode 100644
--- /dev/null
+++ b/mercurial/revlogutils/flagutil.py
@@ -0,0 +1,31 @@
+# flagutils.py - code to deal with revlog flags and their processors
+#
+# Copyright 2016 Remi Chaintron <remi@fb.com>
+# Copyright 2016-2019 Pierre-Yves David <pierre-yves.david@ens-lyon.org>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+from .constants import (
+    REVIDX_DEFAULT_FLAGS,
+    REVIDX_ELLIPSIS,
+    REVIDX_EXTSTORED,
+    REVIDX_FLAGS_ORDER,
+    REVIDX_ISCENSORED,
+    REVIDX_KNOWN_FLAGS,
+    REVIDX_RAWTEXT_CHANGING_FLAGS,
+)
+
+# blanked usage of all the name to prevent pyflakes constraints
+# We need these name available in the module for extensions.
+REVIDX_ISCENSORED
+REVIDX_ELLIPSIS
+REVIDX_EXTSTORED
+REVIDX_DEFAULT_FLAGS
+REVIDX_FLAGS_ORDER
+REVIDX_KNOWN_FLAGS
+REVIDX_RAWTEXT_CHANGING_FLAGS
+
+