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..df355838 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
@@ -51,7 +51,11 @@
  *      (see method @reserveNewBlock)
  *
  * Also, when saving the blocks, we need to check for the block's last committed value.
- * If it's last committed value is same as last value, we should release the block in DB
+ * If its last committed value is same as last value, we should release the block in DB.
+ *
+ * To guarantee safe multiprocessing in PostgreSQL, all methods in ContiguousIdBlockService that access the DB must use
+ * the SERIALIZABLE transaction isolation level.
+ * See here for details: https://wiki.postgresql.org/wiki/Serializable#PostgreSQL_Implementation
  *
  */
 public class ContiguousIdBlockService {
@@ -69,7 +73,7 @@ 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 +81,7 @@ 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()) {