diff --git a/src/main/kotlin/fr/postgresjson/entity/immutable/ImmutableEntity.kt b/src/main/kotlin/fr/postgresjson/entity/immutable/ImmutableEntity.kt
index 9952c51..d9d56b6 100644
--- a/src/main/kotlin/fr/postgresjson/entity/immutable/ImmutableEntity.kt
+++ b/src/main/kotlin/fr/postgresjson/entity/immutable/ImmutableEntity.kt
@@ -26,9 +26,9 @@ interface EntityVersioning<ID, NUMBER> {
 }
 
 class UuidEntityVersioning(
-    override var versionNumber: Int? = null,
+    override val versionNumber: Int,
     versionId: UUID? = null
-) : EntityVersioning<UUID, Int?> {
+) : EntityVersioning<UUID, Int> {
     override val versionId: UUID = versionId ?: UUID.randomUUID()
 }
 
diff --git a/src/main/kotlin/fr/postgresjson/entity/mutable/MutableEntity.kt b/src/main/kotlin/fr/postgresjson/entity/mutable/MutableEntity.kt
index ee7edf3..ea2c74d 100644
--- a/src/main/kotlin/fr/postgresjson/entity/mutable/MutableEntity.kt
+++ b/src/main/kotlin/fr/postgresjson/entity/mutable/MutableEntity.kt
@@ -29,7 +29,7 @@ interface EntityVersioning<ID, NUMBER> {
 class UuidEntityVersioning(
     override var versionNumber: Int? = null,
     versionId: UUID? = null
-) : EntityVersioning<UUID, Int?> {
+) : EntityVersioning<UUID, Int> {
     override var versionId: UUID = versionId ?: UUID.randomUUID()
 }
 
@@ -133,5 +133,5 @@ abstract class UuidEntityExtended<T, UserT : EntityI>(
     publishedBy: UserT?
 ) :
     EntityImp<T, UserT>(updatedBy),
-    EntityVersioning<UUID, Int?> by UuidEntityVersioning(),
+    EntityVersioning<UUID, Int> by UuidEntityVersioning(),
     Published<UserT> by EntityPublishedImp(publishedBy)