diff --git a/CMakeLists.txt b/CMakeLists.txt
index f7deab84..dc694b17 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,7 +24,7 @@
 
 cmake_minimum_required(VERSION 3.0)
 # XXX using 1.8.90 instead of 1.9.0-DEV
-project(nghttp2 VERSION 1.51.0)
+project(nghttp2 VERSION 1.51.90)
 
 # See versioning rule:
 #  https://www.gnu.org/software/libtool/manual/html_node/Updating-version-info.html
diff --git a/configure.ac b/configure.ac
index 8b3678b5..c50515ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,7 +25,7 @@ dnl Do not change user variables!
 dnl https://www.gnu.org/software/automake/manual/html_node/Flag-Variables-Ordering.html
 
 AC_PREREQ(2.61)
-AC_INIT([nghttp2], [1.51.0], [t-tujikawa@users.sourceforge.net])
+AC_INIT([nghttp2], [1.52.0-DEV], [t-tujikawa@users.sourceforge.net])
 AC_CONFIG_AUX_DIR([.])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])