diff --git a/build.gradle b/build.gradle
index 87085effb7..68a503520e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -108,7 +108,7 @@ subprojects {
     apply plugin: 'de.thetaphi.forbiddenapis'
     apply plugin: 'com.github.spotbugs'
 
-    version = '5.1.0'
+    version = '5.1.1-SNAPSHOT'
     ext {
         bouncyCastleVersion = '1.69'
         commonsCodecVersion = '1.15'
diff --git a/build.xml b/build.xml
index 42d5cc58c3..b83c0acba2 100644
--- a/build.xml
+++ b/build.xml
@@ -42,7 +42,7 @@ under the License.
 
     <description>The Apache POI project Ant build.</description>
 
-    <property name="version.id" value="5.1.0"/>
+    <property name="version.id" value="5.1.1-SNAPSHOT"/>
     <property name="release.rc" value=""/>
 
     <property environment="env"/>