diff --git a/platform/workspace/storage/src/com/intellij/platform/workspace/storage/impl/AddDiffOperation.kt b/platform/workspace/storage/src/com/intellij/platform/workspace/storage/impl/AddDiffOperation.kt
index bff290ab248d..b33b185bcd3b 100644
--- a/platform/workspace/storage/src/com/intellij/platform/workspace/storage/impl/AddDiffOperation.kt
+++ b/platform/workspace/storage/src/com/intellij/platform/workspace/storage/impl/AddDiffOperation.kt
@@ -127,7 +127,7 @@ internal class AddDiffOperation(val target: MutableEntityStorageImpl, val diff:
       if (targetParentId != null) {
 
         // For one-to-one connections it's necessary to remove the obsolete children to avoid "entity leaks" and the state of broken store
-        if (connectionId.connectionType == ConnectionId.ConnectionType.ONE_TO_ONE || connectionId.connectionType == ConnectionId.ConnectionType.ABSTRACT_ONE_TO_ONE) {
+        if (connectionId.isOneToOne && !connectionId.isParentNullable) {
           val obsoleteChild = target.extractOneToOneChild<WorkspaceEntityBase>(connectionId, targetParentId.id)
           if (obsoleteChild != null && obsoleteChild.id != targetEntityId.id) {
             target.removeEntity(obsoleteChild)
diff --git a/platform/workspace/storage/tests/testSrc/com/intellij/platform/workspace/storage/tests/AddDiffTest.kt b/platform/workspace/storage/tests/testSrc/com/intellij/platform/workspace/storage/tests/AddDiffTest.kt
index 999f96ecfb48..651a97ea6a3b 100644
--- a/platform/workspace/storage/tests/testSrc/com/intellij/platform/workspace/storage/tests/AddDiffTest.kt
+++ b/platform/workspace/storage/tests/testSrc/com/intellij/platform/workspace/storage/tests/AddDiffTest.kt
@@ -731,6 +731,50 @@ class AddDiffTest {
     assertTrue(target.entities(XChildWithOptionalParentEntity::class.java).none())
   }
 
+  @RepeatedTest(10)
+  fun `replace child by modification`() {
+    val parentEntity = target addEntity OoParentEntity("Parent2", MySource) {
+      this.anotherChild = OoChildWithNullableParentEntity(MySource)
+    }
+
+    val source = createBuilderFrom(target)
+    source.modifyEntity(parentEntity.from(source)) {
+      this.anotherChild = OoChildWithNullableParentEntity(AnotherSource)
+    }
+
+    // The previous child was not removed because it has optional parent
+    assertEquals(2, source.entities(OoChildWithNullableParentEntity::class.java).toList().size)
+
+    target.addDiff(source)
+
+    target.assertConsistency()
+
+    assertEquals(AnotherSource, target.entities(OoParentEntity::class.java).single().anotherChild!!.entitySource)
+    assertEquals(2, target.entities(OoChildWithNullableParentEntity::class.java).toList().size)
+  }
+
+  @RepeatedTest(10)
+  fun `add child with parallel update`() {
+    val parentEntity = target addEntity OoParentEntity("Parent2", MySource)
+
+    val source = createBuilderFrom(target)
+    source.modifyEntity(parentEntity.from(source)) {
+      this.anotherChild = OoChildWithNullableParentEntity(AnotherSource)
+    }
+
+    // Update target builder in parallel with the source builder
+    target.modifyEntity(parentEntity.from(source)) {
+      this.anotherChild = OoChildWithNullableParentEntity(MySource)
+    }
+
+    target.addDiff(source)
+
+    target.assertConsistency()
+
+    assertEquals(AnotherSource, target.entities(OoParentEntity::class.java).single().anotherChild!!.entitySource)
+    assertEquals(2, target.entities(OoChildWithNullableParentEntity::class.java).toList().size)
+  }
+
   @RepeatedTest(10)
   fun `remove entity with soft link`() {
     val entity = target addEntity WithSoftLinkEntity(NameId("id"), MySource)