diff --git a/examples/notebook/package.json b/examples/notebook/package.json
index 994b21b2783d..6e1229e52e10 100644
--- a/examples/notebook/package.json
+++ b/examples/notebook/package.json
@@ -12,11 +12,11 @@
     "@jupyterlab/completer": "^0.19.1",
     "@jupyterlab/docmanager": "^0.19.1",
     "@jupyterlab/docregistry": "^0.19.1",
+    "@jupyterlab/mathjax2": "^0.7.1",
     "@jupyterlab/notebook": "^0.19.2",
     "@jupyterlab/rendermime": "^0.19.1",
     "@jupyterlab/services": "^3.2.1",
     "@jupyterlab/theme-light-extension": "^0.19.1",
-    "@jupyterlab/mathjax2": "^0.7.1",
     "@phosphor/commands": "^1.6.1",
     "@phosphor/widgets": "^1.6.0",
     "es6-promise": "~4.1.1"
diff --git a/packages/cells/src/celldragutils.ts b/packages/cells/src/celldragutils.ts
index fd6e7cc1309c..d67bd588df2f 100644
--- a/packages/cells/src/celldragutils.ts
+++ b/packages/cells/src/celldragutils.ts
@@ -13,7 +13,7 @@ import { each, IterableOrArrayLike } from '@phosphor/algorithm';
 import { ICodeCellModel } from './model';
 import { Cell } from './widget';
 import { h, VirtualDOM } from '@phosphor/virtualdom';
-import { nbformat } from '../../coreutils/lib';
+import { nbformat } from '@jupyterlab/coreutils';
 
 /**
  * Constants for drag
@@ -60,6 +60,9 @@ export namespace CellDragUtils {
    * @param cells - an iterable of Cells
    * @param isCellNode - a function that takes in a node and checks if
    * it is a cell node.
+   *
+   * @returns index of the cell we're looking for. Returns -1 if
+   * the cell is not founds
    */
   export function findCell(
     node: HTMLElement,
diff --git a/packages/console/src/widget.ts b/packages/console/src/widget.ts
index 3fcd06dae6bb..0e4a2c8b4bb3 100644
--- a/packages/console/src/widget.ts
+++ b/packages/console/src/widget.ts
@@ -421,6 +421,10 @@ export class CodeConsole extends Widget {
       cellIndex = CellDragUtils.findCell(target, this._cells, cellFilter);
     }
 
+    if (cellIndex === -1) {
+      return;
+    }
+
     const cell = this._cells.get(cellIndex);
 
     let targetArea: CellDragUtils.ICellTargetArea = CellDragUtils.detectTargetArea(
@@ -435,7 +439,7 @@ export class CodeConsole extends Widget {
         index: cellIndex
       };
 
-      this._focussedCell = cell;
+      this._focusedCell = cell;
 
       document.addEventListener('mouseup', this, true);
       document.addEventListener('mousemove', this, true);
@@ -464,11 +468,11 @@ export class CodeConsole extends Widget {
    * Start a drag event
    */
   private _startDrag(index: number, clientX: number, clientY: number) {
-    const cellModel = this._focussedCell.model as ICodeCellModel;
+    const cellModel = this._focusedCell.model as ICodeCellModel;
     let selected: nbformat.ICell[] = [cellModel.toJSON()];
 
     const dragImage = CellDragUtils.createCellDragImage(
-      this._focussedCell,
+      this._focusedCell,
       selected
     );
 
@@ -484,7 +488,7 @@ export class CodeConsole extends Widget {
     const textContent = cellModel.value.text;
     this._drag.mimeData.setData('text/plain', textContent);
 
-    this._focussedCell = null;
+    this._focusedCell = null;
 
     document.removeEventListener('mousemove', this, true);
     document.removeEventListener('mouseup', this, true);
@@ -817,7 +821,7 @@ export class CodeConsole extends Widget {
   private _promptCellCreated = new Signal<this, CodeCell>(this);
   private _dragData: { pressX: number; pressY: number; index: number } = null;
   private _drag: Drag = null;
-  private _focussedCell: Cell = null;
+  private _focusedCell: Cell = null;
 }
 
 /**