diff --git a/README.md b/README.md
index bf28015f400..0a388b0a77c 100644
--- a/README.md
+++ b/README.md
@@ -409,7 +409,7 @@ More details can be found in [CONTRIBUTING](CONTRIBUTING.md).
 
 ## Change Log
 
-### 18.3a5 (unreleased)
+### 18.4a0
 
 * added `--diff` (#87)
 
diff --git a/black.py b/black.py
index 2c61880dda2..6bb29feea43 100644
--- a/black.py
+++ b/black.py
@@ -38,7 +38,7 @@
 from blib2to3.pgen2 import driver, token
 from blib2to3.pgen2.parse import ParseError
 
-__version__ = "18.3a4"
+__version__ = "18.4a0"
 DEFAULT_LINE_LENGTH = 88
 # types
 syms = pygram.python_symbols