diff --git a/wallabyjs/index.d.ts b/wallabyjs/index.d.ts
index 7b791e44ff..6c4d332de0 100644
--- a/wallabyjs/index.d.ts
+++ b/wallabyjs/index.d.ts
@@ -11,7 +11,7 @@ declare module 'wallabyjs' {
    *
    * @property {IWallabyCompiler=}     compilers - File patterns as keys and compiler functions as values.
    * @property {boolean=}              debug - Flag if debug messages written to Wallaby console (default=false).
-   * @prooperty {IWallabyEnvironment=} env - Specify a different test runner or change the runner settings.
+   * @property {IWallabyEnvironment=} env - Specify a different test runner or change the runner settings.
    * @property {string[] | IWallabyFilePattern[]}   files - Specifies an array of source files or file name patterns to copy
    *                                                        to the local cache.
    * @property {Function=}             postprocessor - Function that runs for every batch of file changes after all compilers and preprocessors.
@@ -155,6 +155,7 @@ declare module 'wallabyjs' {
     params?: IWallabyEnvironmentParameters;
     runner?: string;
     type?: string;
+    viewportSize?: IWallabyEnvironmentViewportSize
   }
 
   /**
@@ -172,6 +173,19 @@ declare module 'wallabyjs' {
     runner?: string;
   }
 
+  /**
+   * Wallaby viewport settings for testing.
+   *
+   * @interface IWallabyEnvironmentViewportSize
+   *
+   * @property  {number=} width - Width in pixels for the viewport size in PhantomJs/Electron.
+   * @property  {number=} height - height in pixels for the viewport size in PhantomJs/Electron.
+   */
+  export interface IWallabyEnvironmentViewportSize {
+    width?: number;
+    height?: number;
+  }
+
   /**
    * Wallaby worker configuration.
    *
diff --git a/wallabyjs/wallabyjs-tests.ts b/wallabyjs/wallabyjs-tests.ts
index 5fd8344797..5e6c90e0a4 100644
--- a/wallabyjs/wallabyjs-tests.ts
+++ b/wallabyjs/wallabyjs-tests.ts
@@ -31,6 +31,9 @@ export class WallabyConfig implements wallabyjs.IWallabyConfig {
     params:  {
       env: 'KEY1=value1;KEY2=value2',
       runner: '--arg1;--arg2;'
+    },
+    viewportSize: {
+      width: 800
     }
   };