diff --git a/Lib/fontTools/__init__.py b/Lib/fontTools/__init__.py
index 502ca5cec..7b13574dd 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__ = "4.55.0"
+version = __version__ = "4.55.1.dev0"
 
 __all__ = ["version", "log", "configLogger"]
diff --git a/setup.cfg b/setup.cfg
index 868a84822..bdc4ba15b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -1,5 +1,5 @@
 [bumpversion]
-current_version = 4.55.0
+current_version = 4.55.1.dev0
 commit = True
 tag = False
 tag_name = {new_version}
diff --git a/setup.py b/setup.py
index 2076bca07..cc6f0df4a 100755
--- a/setup.py
+++ b/setup.py
@@ -482,7 +482,7 @@ if ext_modules:
 
 setup_params = dict(
     name="fonttools",
-    version="4.55.0",
+    version="4.55.1.dev0",
     description="Tools to manipulate font files",
     author="Just van Rossum",
     author_email="just@letterror.com",