diff --git a/src/browser/input/Mouse.test.ts b/src/browser/input/Mouse.test.ts
index 6a908499..00260361 100644
--- a/src/browser/input/Mouse.test.ts
+++ b/src/browser/input/Mouse.test.ts
@@ -11,30 +11,38 @@ const CHAR_WIDTH = 10;
 const CHAR_HEIGHT = 20;
 
 describe('Mouse getCoords', () => {
+  let windowOverride: Pick<Window, 'getComputedStyle'>;
   let document: Document;
 
   beforeEach(() => {
+    windowOverride = {
+      getComputedStyle(): any {
+        return {
+          getPropertyValue: () => '0px'
+        } as Pick<CSSStyleDeclaration, 'getPropertyValue'>;
+      }
+    };
     document = new jsdom.JSDOM('').window.document;
   });
 
   it('should return the cell that was clicked', () => {
     let coords: [number, number] | undefined;
-    coords = getCoords({ clientX: CHAR_WIDTH / 2, clientY: CHAR_HEIGHT / 2 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: CHAR_WIDTH / 2, clientY: CHAR_HEIGHT / 2 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [1, 1]);
-    coords = getCoords({ clientX: CHAR_WIDTH, clientY: CHAR_HEIGHT }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: CHAR_WIDTH, clientY: CHAR_HEIGHT }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [1, 1]);
-    coords = getCoords({ clientX: CHAR_WIDTH, clientY: CHAR_HEIGHT + 1 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: CHAR_WIDTH, clientY: CHAR_HEIGHT + 1 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [1, 2]);
-    coords = getCoords({ clientX: CHAR_WIDTH + 1, clientY: CHAR_HEIGHT }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: CHAR_WIDTH + 1, clientY: CHAR_HEIGHT }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [2, 1]);
   });
 
   it('should ensure the coordinates are returned within the terminal bounds', () => {
     let coords: [number, number] | undefined;
-    coords = getCoords({ clientX: -1, clientY: -1 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: -1, clientY: -1 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [1, 1]);
     // Event are double the cols/rows
-    coords = getCoords({ clientX: CHAR_WIDTH * 20, clientY: CHAR_HEIGHT * 20 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
+    coords = getCoords(windowOverride, { clientX: CHAR_WIDTH * 20, clientY: CHAR_HEIGHT * 20 }, document.createElement('div'), 10, 10, true, CHAR_WIDTH, CHAR_HEIGHT);
     assert.deepEqual(coords, [10, 10], 'coordinates should never come back as larger than the terminal');
   });
 });
diff --git a/src/browser/input/Mouse.ts b/src/browser/input/Mouse.ts
index 31a6af0a..6c377edb 100644
--- a/src/browser/input/Mouse.ts
+++ b/src/browser/input/Mouse.ts
@@ -3,7 +3,7 @@
  * @license MIT
  */
 
-export function getCoordsRelativeToElement(event: {clientX: number, clientY: number}, element: HTMLElement): [number, number] {
+export function getCoordsRelativeToElement(window: Pick<Window, 'getComputedStyle'>, event: {clientX: number, clientY: number}, element: HTMLElement): [number, number] {
   const rect = element.getBoundingClientRect();
   const elementStyle = window.getComputedStyle(element);
   const leftPadding = parseInt(elementStyle.getPropertyValue('padding-left'));
@@ -26,13 +26,13 @@ export function getCoordsRelativeToElement(event: {clientX: number, clientY: num
  * apply an offset to the x value such that the left half of the cell will
  * select that cell and the right half will select the next cell.
  */
-export function getCoords(event: {clientX: number, clientY: number}, element: HTMLElement, colCount: number, rowCount: number, hasValidCharSize: boolean, actualCellWidth: number, actualCellHeight: number, isSelection?: boolean): [number, number] | undefined {
+export function getCoords(window: Pick<Window, 'getComputedStyle'>, event: {clientX: number, clientY: number}, element: HTMLElement, colCount: number, rowCount: number, hasValidCharSize: boolean, actualCellWidth: number, actualCellHeight: number, isSelection?: boolean): [number, number] | undefined {
   // Coordinates cannot be measured if there are no valid
   if (!hasValidCharSize) {
     return undefined;
   }
 
-  const coords = getCoordsRelativeToElement(event, element);
+  const coords = getCoordsRelativeToElement(window, event, element);
   if (!coords) {
     return undefined;
   }
diff --git a/src/browser/services/MouseService.ts b/src/browser/services/MouseService.ts
index 348ba64e..69123ba3 100644
--- a/src/browser/services/MouseService.ts
+++ b/src/browser/services/MouseService.ts
@@ -17,6 +17,7 @@ export class MouseService implements IMouseService {
 
   public getCoords(event: {clientX: number, clientY: number}, element: HTMLElement, colCount: number, rowCount: number, isSelection?: boolean): [number, number] | undefined {
     return getCoords(
+      window,
       event,
       element,
       colCount,
diff --git a/src/browser/services/SelectionService.ts b/src/browser/services/SelectionService.ts
index c7b7707a..57ba048f 100644
--- a/src/browser/services/SelectionService.ts
+++ b/src/browser/services/SelectionService.ts
@@ -402,7 +402,7 @@ export class SelectionService extends Disposable implements ISelectionService {
    * @param event The mouse event.
    */
   private _getMouseEventScrollAmount(event: MouseEvent): number {
-    let offset = getCoordsRelativeToElement(event, this._screenElement)[1];
+    let offset = getCoordsRelativeToElement(window, event, this._screenElement)[1];
     const terminalHeight = this._renderService.dimensions.canvasHeight;
     if (offset >= 0 && offset <= terminalHeight) {
       return 0;