diff --git a/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookCellInlayManager.kt b/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookCellInlayManager.kt
index 3ec4bad1fb57..2c8536c266e5 100644
--- a/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookCellInlayManager.kt
+++ b/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookCellInlayManager.kt
@@ -354,7 +354,7 @@ class NotebookCellInlayManager private constructor(
       return CELL_INLAY_MANAGER_KEY.get(editor)
     }
 
-    val FOLDING_MARKER_KEY: Key<Boolean> = Key<Boolean>("jupyter.folding.paragraph")
+    val FOLDING_MARKER_KEY: Key<Boolean> = Key("jupyter.folding.paragraph")
     private val CELL_INLAY_MANAGER_KEY = Key.create<NotebookCellInlayManager>(NotebookCellInlayManager::class.java.name)
   }
 
@@ -381,10 +381,16 @@ class NotebookCellInlayManager private constructor(
             change.subsequentPointers.forEach {
               addCell(it.pointer)
             }
+
             //After insert, we need fix ranges of previous cell
             change.subsequentPointers.forEach {
-              val prevCell = getCellOrNull(it.interval.ordinal - 1)
-              prevCell?.checkAndRebuildInlays()
+              getCellOrNull(it.interval.ordinal - 1)?.checkAndRebuildInlays()
+            }
+
+            // When we are inserting a new 'first cell', we need to update AboveCellDelimiterPanel
+            // for the old 'first' cell.
+            if (change.ordinals.contains(0)) {
+              getCellOrNull(change.ordinals.last + 1)?.checkAndRebuildInlays()
             }
           }
           is NotebookIntervalPointersEvent.OnRemoved -> {
diff --git a/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookIntervalPointersEvent.kt b/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookIntervalPointersEvent.kt
index 8517de0b496d..0c3809be987c 100644
--- a/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookIntervalPointersEvent.kt
+++ b/notebooks/visualization/src/com/intellij/notebooks/visualization/NotebookIntervalPointersEvent.kt
@@ -1,12 +1,12 @@
 package com.intellij.notebooks.visualization
 
 /**
- * passed to [NotebookIntervalPointerFactory.ChangeListener] in next cases:
- * * Underlying document is changed. (in such case cellLinesEvent != null)
+ * Passed to [NotebookIntervalPointerFactory.ChangeListener] in next cases:
+ * * Underlying document is changed. (in such cases cellLinesEvent != null)
  * * Someone explicitly swapped two pointers or invalidated them by calling [NotebookIntervalPointerFactory.modifyPointers]
  * * one of upper changes was reverted or redone.
  *
- * Changes represented as list of trivial changes. [Change]
+ * Changes represented as a list of trivial changes. [Change]
  * Intervals which was just moved are not mentioned in changes. For example, when inserting code before them.
  */
 data class NotebookIntervalPointersEvent(val isInBulkUpdate: Boolean,val changes: List<Change>) {
@@ -15,17 +15,17 @@ data class NotebookIntervalPointersEvent(val isInBulkUpdate: Boolean,val changes
   data class PointerSnapshot(val pointer: NotebookIntervalPointer, val interval: NotebookCellLines.Interval)
 
   /**
-   * any change contains enough information to be inverted. It simplifies undo/redo actions.
+   * Any change contains enough information to be inverted. It simplifies undo/redo actions.
    */
   sealed interface Change
 
   data class OnInserted(val subsequentPointers: List<PointerSnapshot>) : Change {
-    val ordinals = subsequentPointers.first().interval.ordinal..subsequentPointers.last().interval.ordinal
+    val ordinals: IntRange = subsequentPointers.first().interval.ordinal..subsequentPointers.last().interval.ordinal
   }
 
-  /* snapshots contains intervals before removal */
+  /* Snapshots contain intervals before removal */
   data class OnRemoved(val subsequentPointers: List<PointerSnapshot>) : Change {
-    val ordinals = subsequentPointers.first().interval.ordinal..subsequentPointers.last().interval.ordinal
+    val ordinals: IntRange = subsequentPointers.first().interval.ordinal..subsequentPointers.last().interval.ordinal
   }
 
   data class OnEdited(val pointer: NotebookIntervalPointer,
@@ -35,7 +35,7 @@ data class NotebookIntervalPointersEvent(val isInBulkUpdate: Boolean,val changes
       get() = intervalAfter.ordinal
   }
 
-  /* snapshots contains intervals after swap */
+  /* Snapshots contain intervals after swap */
   data class OnSwapped(val first: PointerSnapshot, val second: PointerSnapshot) : Change {
     val firstOrdinal: Int
       get() = first.interval.ordinal