diff --git a/src/cdk/testing/protractor/protractor-element.ts b/src/cdk/testing/protractor/protractor-element.ts
index 7167f45363f0..501b75431ce8 100644
--- a/src/cdk/testing/protractor/protractor-element.ts
+++ b/src/cdk/testing/protractor/protractor-element.ts
@@ -6,7 +6,13 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ElementDimensions, ModifierKeys, TestElement, TestKey} from '@angular/cdk/testing';
+import {
+  ElementDimensions,
+  getNoKeysSpecifiedError,
+  ModifierKeys,
+  TestElement,
+  TestKey
+} from '@angular/cdk/testing';
 import {browser, ElementFinder, Key} from 'protractor';
 
 /** Maps the `TestKey` constants to Protractor's `Key` constants. */
@@ -100,7 +106,7 @@ export class ProtractorElement implements TestElement {
     const first = modifiersAndKeys[0];
     let modifiers: ModifierKeys;
     let rest: (string | TestKey)[];
-    if (typeof first !== 'string' && typeof first !== 'number') {
+    if (first !== undefined && typeof first !== 'string' && typeof first !== 'number') {
       modifiers = first;
       rest = modifiersAndKeys.slice(1);
     } else {
@@ -113,6 +119,12 @@ export class ProtractorElement implements TestElement {
         .reduce((arr, k) => arr.concat(k), [])
         .map(k => Key.chord(...modifierKeys, k));
 
+    // Throw an error if no keys have been specified. Calling this function with no
+    // keys should not result in a focus event being dispatched unexpectedly.
+    if (keys.length === 0) {
+      throw getNoKeysSpecifiedError();
+    }
+
     return this.element.sendKeys(...keys);
   }
 
diff --git a/src/cdk/testing/test-element.ts b/src/cdk/testing/test-element.ts
index 6c0329ea6e4b..762c650ac661 100644
--- a/src/cdk/testing/test-element.ts
+++ b/src/cdk/testing/test-element.ts
@@ -84,13 +84,13 @@ export interface TestElement {
 
   /**
    * Sends the given string to the input as a series of key presses. Also fires input events
-   * and attempts to add the string to the Element's value.
+   * and attempts to add the string to the Element's value. Throws if no keys have been specified.
    */
   sendKeys(...keys: (string | TestKey)[]): Promise<void>;
 
   /**
    * Sends the given string to the input as a series of key presses. Also fires input events
-   * and attempts to add the string to the Element's value.
+   * and attempts to add the string to the Element's value. Throws if no keys have been specified.
    */
   sendKeys(modifiers: ModifierKeys, ...keys: (string | TestKey)[]): Promise<void>;
 
@@ -115,3 +115,11 @@ export interface TestElement {
   /** Checks whether the element is focused. */
   isFocused(): Promise<boolean>;
 }
+
+/**
+ * Returns an error which reports that no keys have been specified.
+ * @docs-private
+ */
+export function getNoKeysSpecifiedError() {
+  return Error('No keys have been specified.');
+}
diff --git a/src/cdk/testing/testbed/fake-events/type-in-element.ts b/src/cdk/testing/testbed/fake-events/type-in-element.ts
index 41e715a95ac6..703bd6670276 100644
--- a/src/cdk/testing/testbed/fake-events/type-in-element.ts
+++ b/src/cdk/testing/testbed/fake-events/type-in-element.ts
@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ModifierKeys} from '@angular/cdk/testing';
+import {getNoKeysSpecifiedError, ModifierKeys} from '@angular/cdk/testing';
 import {dispatchFakeEvent, dispatchKeyboardEvent} from './dispatch-events';
 import {triggerFocus} from './element-focus';
 
@@ -20,7 +20,7 @@ export function isTextInput(element: Element): element is HTMLInputElement | HTM
 }
 
 /**
- * Focuses an input, sets its value and dispatches
+ * If keys have been specified, focuses an input, sets its value and dispatches
  * the `input` event, simulating the user typing.
  * @param element Element onto which to set the value.
  * @param keys The keys to send to the element.
@@ -30,7 +30,7 @@ export function typeInElement(
     element: HTMLElement, ...keys: (string | {keyCode?: number, key?: string})[]): void;
 
 /**
- * Focuses an input, sets its value and dispatches
+ * If keys have been specified, focuses an input, sets its value and dispatches
  * the `input` event, simulating the user typing.
  * @param element Element onto which to set the value.
  * @param modifiers Modifier keys that are held while typing.
@@ -40,11 +40,12 @@ export function typeInElement(
 export function typeInElement(element: HTMLElement, modifiers: ModifierKeys,
                               ...keys: (string | {keyCode?: number, key?: string})[]): void;
 
-export function typeInElement(element: HTMLElement, ...modifiersAndKeys: any) {
+export function typeInElement(element: HTMLElement, ...modifiersAndKeys: any[]) {
   const first = modifiersAndKeys[0];
   let modifiers: ModifierKeys;
   let rest: (string | {keyCode?: number, key?: string})[];
-  if (typeof first !== 'string' && first.keyCode === undefined && first.key === undefined) {
+  if (first !== undefined && typeof first !== 'string' && first.keyCode === undefined &&
+      first.key === undefined) {
     modifiers = first;
     rest = modifiersAndKeys.slice(1);
   } else {
@@ -56,6 +57,12 @@ export function typeInElement(element: HTMLElement, ...modifiersAndKeys: any) {
           k.split('').map(c => ({keyCode: c.toUpperCase().charCodeAt(0), key: c})) : [k])
       .reduce((arr, k) => arr.concat(k), []);
 
+  // Throw an error if no keys have been specified. Calling this function with no
+  // keys should not result in a focus event being dispatched unexpectedly.
+  if (keys.length === 0) {
+    throw getNoKeysSpecifiedError();
+  }
+
   triggerFocus(element);
   for (const key of keys) {
     dispatchKeyboardEvent(element, 'keydown', key.keyCode, key.key, element, modifiers);
diff --git a/src/cdk/testing/tests/protractor.e2e.spec.ts b/src/cdk/testing/tests/protractor.e2e.spec.ts
index af5ca877f160..720a79f3ac91 100644
--- a/src/cdk/testing/tests/protractor.e2e.spec.ts
+++ b/src/cdk/testing/tests/protractor.e2e.spec.ts
@@ -1,6 +1,7 @@
 import {
   ComponentHarness,
   ComponentHarnessConstructor,
+  getNoKeysSpecifiedError,
   HarnessLoader,
   TestElement
 } from '@angular/cdk/testing';
@@ -197,6 +198,13 @@ describe('ProtractorHarnessEnvironment', () => {
       expect(await input.getProperty('value')).toBe('');
     });
 
+    it('sendKeys method should throw if no keys have been specified', async () => {
+      const input = await harness.input();
+      await expectAsyncError(() => input.sendKeys(), getNoKeysSpecifiedError().toString());
+      await expectAsyncError(() => input.sendKeys(''), getNoKeysSpecifiedError().toString());
+      await expectAsyncError(() => input.sendKeys('', ''), getNoKeysSpecifiedError().toString());
+    });
+
     it('should be able to click', async () => {
       const counter = await harness.counter();
       expect(await counter.text()).toBe('0');
diff --git a/src/cdk/testing/tests/testbed.spec.ts b/src/cdk/testing/tests/testbed.spec.ts
index ee9cc26e6104..e8519025aee8 100644
--- a/src/cdk/testing/tests/testbed.spec.ts
+++ b/src/cdk/testing/tests/testbed.spec.ts
@@ -1,6 +1,7 @@
 import {
   ComponentHarness,
   ComponentHarnessConstructor,
+  getNoKeysSpecifiedError,
   HarnessLoader,
   TestElement
 } from '@angular/cdk/testing';
@@ -16,7 +17,6 @@ import {TestMainComponent} from './test-main-component';
 function activeElementText() {
   return document.activeElement && (document.activeElement as HTMLElement).innerText || '';
 }
-
 describe('TestbedHarnessEnvironment', () => {
   let fixture: ComponentFixture<{}>;
 
@@ -294,6 +294,13 @@ describe('TestbedHarnessEnvironment', () => {
       expect(await input.getProperty('value')).toBe('');
     });
 
+    it('sendKeys method should throw if no keys have been specified', async () => {
+      const input = await harness.input();
+      await expectAsyncError(() => input.sendKeys(), getNoKeysSpecifiedError().toString());
+      await expectAsyncError(() => input.sendKeys(''), getNoKeysSpecifiedError().toString());
+      await expectAsyncError(() => input.sendKeys('', ''), getNoKeysSpecifiedError().toString());
+    });
+
     it('should be able to click', async () => {
       const counter = await harness.counter();
       expect(await counter.text()).toBe('0');