diff --git a/Lib/fontTools/__init__.py b/Lib/fontTools/__init__.py
index 815b82b2c..3f259ae5a 100644
--- a/Lib/fontTools/__init__.py
+++ b/Lib/fontTools/__init__.py
@@ -3,6 +3,6 @@ from fontTools.misc.loggingTools import configLogger
 
 log = logging.getLogger(__name__)
 
-version = __version__ = "4.39.3"
+version = __version__ = "4.39.4.dev0"
 
 __all__ = ["version", "log", "configLogger"]
diff --git a/setup.cfg b/setup.cfg
index d36773c77..05bf46b0d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 4.39.3
+current_version = 4.39.4.dev0
 commit = True
 tag = False
 tag_name = {new_version}
diff --git a/setup.py b/setup.py
index e47a0d460..7c704fe35 100755
--- a/setup.py
+++ b/setup.py
@@ -467,7 +467,7 @@ if ext_modules:
 
 setup_params = dict(
     name="fonttools",
-    version="4.39.3",
+    version="4.39.4.dev0",
     description="Tools to manipulate font files",
     author="Just van Rossum",
     author_email="just@letterror.com",