diff --git a/accession-commons-monotonic-generator-jpa/src/main/java/uk/ac/ebi/ampt2d/commons/accession/persistence/jpa/monotonic/service/ContiguousIdBlockService.java b/accession-commons-monotonic-generator-jpa/src/main/java/uk/ac/ebi/ampt2d/commons/accession/persistence/jpa/monotonic/service/ContiguousIdBlockService.java
index 5f86d4e0..37a456d3 100644
--- a/accession-commons-monotonic-generator-jpa/src/main/java/uk/ac/ebi/ampt2d/commons/accession/persistence/jpa/monotonic/service/ContiguousIdBlockService.java
+++ b/accession-commons-monotonic-generator-jpa/src/main/java/uk/ac/ebi/ampt2d/commons/accession/persistence/jpa/monotonic/service/ContiguousIdBlockService.java
@@ -69,7 +69,7 @@ public ContiguousIdBlockService(ContiguousIdBlockRepository repository, Map<Stri
         this.categoryBlockInitializations = categoryBlockInitializations;
     }
 
-    @Transactional
+    @Transactional(isolation = Isolation.SERIALIZABLE)
     public void save(Iterable<ContiguousIdBlock> blocks) {
         // release block if full
         blocks.forEach(block -> {if (block.isFull()) {block.releaseReserved();}});
@@ -77,7 +77,7 @@ public void save(Iterable<ContiguousIdBlock> blocks) {
         entityManager.flush();
     }
 
-    @Transactional
+    @Transactional(isolation = Isolation.SERIALIZABLE)
     public void save(ContiguousIdBlock block) {
         // release block if full
         if (block.isFull()) {