diff --git a/services/src/main/java/org/keycloak/services/resources/admin/UserStorageProviderResource.java b/services/src/main/java/org/keycloak/services/resources/admin/UserStorageProviderResource.java
index 672822b6c0..74962754da 100644
--- a/services/src/main/java/org/keycloak/services/resources/admin/UserStorageProviderResource.java
+++ b/services/src/main/java/org/keycloak/services/resources/admin/UserStorageProviderResource.java
@@ -142,8 +142,12 @@ public class UserStorageProviderResource {
             syncResult = syncManager.syncAllUsers(session.getKeycloakSessionFactory(), realm.getId(), providerModel);
         } else if ("triggerChangedUsersSync".equals(action)) {
             syncResult = syncManager.syncChangedUsers(session.getKeycloakSessionFactory(), realm.getId(), providerModel);
+        } else if (action == null || action == "") {
+            logger.debug("Missing action");
+            throw new BadRequestException("Missing action");
         } else {
-            throw new NotFoundException("Unknown action: " + action);
+            logger.debug("Unknown action: " + action);
+            throw new BadRequestException("Unknown action: " + action);
         }
 
         Map<String, Object> eventRep = new HashMap<>();
diff --git a/testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/federation/ldap/LDAPSyncTest.java b/testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/federation/ldap/LDAPSyncTest.java
index 6f56f599cd..2acd075683 100755
--- a/testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/federation/ldap/LDAPSyncTest.java
+++ b/testsuite/integration-arquillian/tests/base/src/test/java/org/keycloak/testsuite/federation/ldap/LDAPSyncTest.java
@@ -28,6 +28,7 @@ import org.junit.runners.MethodSorters;
 import org.keycloak.admin.client.resource.UserResource;
 import org.keycloak.component.ComponentModel;
 import org.keycloak.representations.idm.ComponentRepresentation;
+import org.keycloak.representations.idm.SynchronizationResultRepresentation;
 import org.keycloak.services.managers.UserStorageSyncManager;
 import org.keycloak.storage.ldap.idm.model.LDAPObject;
 import org.keycloak.models.KeycloakSessionFactory;
@@ -47,6 +48,8 @@ import org.keycloak.testsuite.util.WaitUtils;
 
 import static org.keycloak.testsuite.arquillian.DeploymentTargetModifier.AUTH_SERVER_CURRENT;
 
+import javax.ws.rs.BadRequestException;
+
 /**
  * @author <a href="mailto:mposolda@redhat.com">Marek Posolda</a>
  */
@@ -355,4 +358,29 @@ public class LDAPSyncTest extends AbstractLDAPTest {
         });
     }
 
+    // KEYCLOAK-10770 user-storage/{id}/sync should return 400 instead of 404
+    @Test
+    public void test05SyncRestAPIMissingAction() {
+        ComponentRepresentation ldapRep = testRealm().components().component(ldapModelId).toRepresentation();
+
+        try {
+            SynchronizationResultRepresentation syncResultRep = adminClient.realm("test").userStorage().syncUsers( ldapModelId, null);
+            Assert.fail("Should throw 400");
+        } catch (Exception e) {
+            Assert.assertTrue(e instanceof BadRequestException);
+        }
+    }
+
+    // KEYCLOAK-10770 user-storage/{id}/sync should return 400 instead of 404
+    @Test
+    public void test06SyncRestAPIWrongAction() {
+        ComponentRepresentation ldapRep = testRealm().components().component(ldapModelId).toRepresentation();
+
+        try {
+            SynchronizationResultRepresentation syncResultRep = adminClient.realm("test").userStorage().syncUsers( ldapModelId, "wrong action");
+            Assert.fail("Should throw 400");
+        } catch (Exception e) {
+            Assert.assertTrue(e instanceof BadRequestException);
+        }
+    }
 }