diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3b4db03e37..87364646e8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,7 +10,7 @@ project (PIO C)
 # The project version number.
 set(VERSION_MAJOR   2   CACHE STRING "Project major version number.")
 set(VERSION_MINOR   5   CACHE STRING "Project minor version number.")
-set(VERSION_PATCH   8   CACHE STRING "Project patch version number.")
+set(VERSION_PATCH   9   CACHE STRING "Project patch version number.")
 mark_as_advanced(VERSION_MAJOR VERSION_MINOR VERSION_PATCH)
 
 # Create version info in autotools parlance for pio_meta.h.
diff --git a/configure.ac b/configure.ac
index 510832dee5..37569eff38 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2,7 +2,7 @@
 ## Ed Hartnett 8/16/17
 
 # Initialize autoconf and automake.
-AC_INIT(pio, 2.5.8)
+AC_INIT(pio, 2.5.9)
 AC_CONFIG_SRCDIR(src/clib/pio_darray.c)
 AM_INIT_AUTOMAKE([foreign serial-tests])
 
@@ -11,7 +11,7 @@ AM_INIT_AUTOMAKE([foreign serial-tests])
 # AC_DEFINE_UNQUOTED for config.h.
 AC_SUBST([PIO_VERSION_MAJOR]) PIO_VERSION_MAJOR=2
 AC_SUBST([PIO_VERSION_MINOR]) PIO_VERSION_MINOR=5
-AC_SUBST([PIO_VERSION_PATCH]) PIO_VERSION_PATCH=8
+AC_SUBST([PIO_VERSION_PATCH]) PIO_VERSION_PATCH=9
 AC_DEFINE_UNQUOTED([PIO_VERSION_MAJOR], [$PIO_VERSION_MAJOR], [PIO major version])
 AC_DEFINE_UNQUOTED([PIO_VERSION_MINOR], [$PIO_VERSION_MINOR], [PIO minor version])
 AC_DEFINE_UNQUOTED([PIO_VERSION_PATCH], [$PIO_VERSION_PATCH], [PIO patch version])
@@ -19,7 +19,7 @@ AC_DEFINE_UNQUOTED([PIO_VERSION_PATCH], [$PIO_VERSION_PATCH], [PIO patch version
 # Once more for the documentation.
 AC_SUBST([VERSION_MAJOR], [2])
 AC_SUBST([VERSION_MINOR], [5])
-AC_SUBST([VERSION_PATCH], [8])
+AC_SUBST([VERSION_PATCH], [9])
 
 
 # The m4 directory holds macros for autoconf.