diff --git a/CHANGELOG.md b/CHANGELOG.md
index f6741c1..e601cf5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,11 @@ All notable changes in keycloak-group-management will be documented in this file
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.5.6] - 2025-02-25
+
+### Fixed
+- Return 409 conflict for concurrent group membership update
+
 ## [1.5.5] - 2025-02-25
 
 ### Fixed
diff --git a/pom.xml b/pom.xml
index 889ee80..edcb8e4 100644
--- a/pom.xml
+++ b/pom.xml
@@ -25,7 +25,7 @@
         <quarkus.version>3.2.7.Final</quarkus.version>
         <maven.compiler.source>17</maven.compiler.source>
         <maven.compiler.target>17</maven.compiler.target>
-        <agm-version>1.5.5</agm-version>
+        <agm-version>1.5.6</agm-version>
     </properties>
 
     <dependencies>
diff --git a/src/main/java/org/rciam/plugins/groups/services/GroupAdminGroupMember.java b/src/main/java/org/rciam/plugins/groups/services/GroupAdminGroupMember.java
index 2b1ed0f..51b84cd 100644
--- a/src/main/java/org/rciam/plugins/groups/services/GroupAdminGroupMember.java
+++ b/src/main/java/org/rciam/plugins/groups/services/GroupAdminGroupMember.java
@@ -22,6 +22,7 @@
 import org.keycloak.email.EmailException;
 import org.keycloak.models.GroupModel;
 import org.keycloak.models.KeycloakSession;
+import org.keycloak.models.ModelException;
 import org.keycloak.models.RealmModel;
 import org.keycloak.models.UserModel;
 import org.keycloak.models.utils.ModelToRepresentation;
@@ -129,7 +130,7 @@ public Response updateMember(UserGroupMembershipExtensionRepresentation rep) {
             });
         } catch (EmailException e) {
             ServicesLogger.LOGGER.failedToSendEmail(e);
-        } catch (OptimisticLockException | StaleObjectStateException e) {
+        } catch (ModelException | OptimisticLockException | StaleObjectStateException e) {
             e.printStackTrace();
             return Response.status(Response.Status.CONFLICT).entity(String.format("Concurrent modification detected: conflicting group membership update for user %s in group %s.", member.getUser().getUsername(), group.getName())).build();
         }