diff --git a/CMakeLists.txt b/CMakeLists.txt
index 399259685b..5bad53988e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,7 +10,7 @@ endif()
 set (GTSAM_VERSION_MAJOR 4)
 set (GTSAM_VERSION_MINOR 2)
 set (GTSAM_VERSION_PATCH 0)
-set (GTSAM_PRERELEASE_VERSION "")
+set (GTSAM_PRERELEASE_VERSION "a9")
 math (EXPR GTSAM_VERSION_NUMERIC "10000 * ${GTSAM_VERSION_MAJOR} + 100 * ${GTSAM_VERSION_MINOR} + ${GTSAM_VERSION_PATCH}")
 
 if (${GTSAM_VERSION_PATCH} EQUAL 0)