diff --git a/CMakeLists.txt b/CMakeLists.txt
index 90f6db9..575c55b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -25,7 +25,7 @@
 
 cmake_minimum_required(VERSION 3.20)
 # XXX using 0.1.90 instead of 0.2.0-DEV
-project(nghttp3 VERSION 1.5.0)
+project(nghttp3 VERSION 1.5.90)
 
 # 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 777a9fd..552cf31 100644
--- a/configure.ac
+++ b/configure.ac
@@ -23,7 +23,7 @@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 AC_PREREQ(2.61)
-AC_INIT([nghttp3], [1.5.0], [t-tujikawa@users.sourceforge.net])
+AC_INIT([nghttp3], [1.6.0-DEV], [t-tujikawa@users.sourceforge.net])
 AC_CONFIG_AUX_DIR([.])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])