diff --git a/src/utils/Mouse.test.ts b/src/utils/Mouse.test.ts
new file mode 100644
index 000000000..15b68ef2d
--- /dev/null
+++ b/src/utils/Mouse.test.ts
@@ -0,0 +1,62 @@
+/**
+ * @license MIT
+ */
+
+import jsdom = require('jsdom');
+import { assert } from 'chai';
+import { getCoords } from './Mouse';
+import { MockCharMeasure } from './TestUtils.test';
+
+const CHAR_WIDTH = 10;
+const CHAR_HEIGHT = 20;
+
+describe('getCoords', () => {
+  let dom: jsdom.JSDOM;
+  let window: Window;
+  let document: Document;
+
+  let charMeasure: MockCharMeasure;
+
+  beforeEach(() => {
+    dom = new jsdom.JSDOM('');
+    window = dom.window;
+    document = window.document;
+    charMeasure = new MockCharMeasure();
+    charMeasure.width = CHAR_WIDTH;
+    charMeasure.height = CHAR_HEIGHT;
+  });
+
+  describe('when charMeasure is not initialized', () => {
+    it('should return null', () => {
+      charMeasure = new MockCharMeasure();
+      assert.equal(getCoords({ pageX: 0, pageY: 0 }, document.createElement('div'), charMeasure, 1, 10, 10), null);
+    });
+  });
+
+  describe('when pageX/pageY are not supported', () => {
+    it('should return null', () => {
+      assert.equal(getCoords({ pageX: undefined, pageY: undefined }, document.createElement('div'), charMeasure, 1, 10, 10), null);
+    });
+  });
+
+  it('should return the cell that was clicked', () => {
+    let coords: [number, number];
+    coords = getCoords({ pageX: CHAR_WIDTH / 2, pageY: CHAR_HEIGHT / 2 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    coords = getCoords({ pageX: CHAR_WIDTH, pageY: CHAR_HEIGHT }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    coords = getCoords({ pageX: CHAR_WIDTH, pageY: CHAR_HEIGHT + 1 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 2]);
+    coords = getCoords({ pageX: CHAR_WIDTH + 1, pageY: CHAR_HEIGHT }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [2, 1]);
+  });
+
+  it('should ensure the coordinates are returned within the terminal bounds', () => {
+    let coords: [number, number];
+    coords = getCoords({ pageX: -1, pageY: -1 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [1, 1]);
+    // Event are double the cols/rows
+    coords = getCoords({ pageX: CHAR_WIDTH * 20, pageY: CHAR_HEIGHT * 20 }, document.createElement('div'), charMeasure, 1, 10, 10);
+    assert.deepEqual(coords, [11, 11], 'coordinates should never come back as larger than the terminal');
+  });
+});
diff --git a/src/utils/Mouse.ts b/src/utils/Mouse.ts
index 0d433cd6f..3bbad855a 100644
--- a/src/utils/Mouse.ts
+++ b/src/utils/Mouse.ts
@@ -4,7 +4,7 @@
 
 import { ICharMeasure } from '../Interfaces';
 
-export function getCoordsRelativeToElement(event: MouseEvent, element: HTMLElement): [number, number] {
+export function getCoordsRelativeToElement(event: {pageX: number, pageY: number}, element: HTMLElement): [number, number] {
   // Ignore browsers that don't support MouseEvent.pageX
   if (event.pageX == null) {
     return null;
@@ -15,7 +15,7 @@ export function getCoordsRelativeToElement(event: MouseEvent, element: HTMLEleme
 
   // Converts the coordinates from being relative to the document to being
   // relative to the terminal.
-  while (element && element !== self.document.documentElement) {
+  while (element) {
     x -= element.offsetLeft;
     y -= element.offsetTop;
     element = 'offsetParent' in element ? <HTMLElement>element.offsetParent : <HTMLElement>element.parentElement;
@@ -36,7 +36,7 @@ export function getCoordsRelativeToElement(event: MouseEvent, element: HTMLEleme
  * 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: MouseEvent, element: HTMLElement, charMeasure: ICharMeasure, lineHeight: number, colCount: number, rowCount: number, isSelection?: boolean): [number, number] {
+export function getCoords(event: {pageX: number, pageY: number}, element: HTMLElement, charMeasure: ICharMeasure, lineHeight: number, colCount: number, rowCount: number, isSelection?: boolean): [number, number] {
   // Coordinates cannot be measured if charMeasure has not been initialized
   if (!charMeasure.width || !charMeasure.height) {
     return null;
diff --git a/src/utils/TestUtils.test.ts b/src/utils/TestUtils.test.ts
index 51f191a83..ed0a19fbe 100644
--- a/src/utils/TestUtils.test.ts
+++ b/src/utils/TestUtils.test.ts
@@ -68,6 +68,14 @@ export class MockTerminal implements ITerminal {
   }
 }
 
+export class MockCharMeasure implements ICharMeasure {
+  width: number;
+  height: number;
+  measure(options: ITerminalOptions): void {
+    throw new Error('Method not implemented.');
+  }
+}
+
 export class MockInputHandlingTerminal implements IInputHandlingTerminal {
   element: HTMLElement;
   options: ITerminalOptions = {};