diff --git a/doc-src/certinstall.html b/doc-src/certinstall.html
index d1435720c..fb3cfd42e 100644
--- a/doc-src/certinstall.html
+++ b/doc-src/certinstall.html
@@ -23,7 +23,7 @@ configure your target device with the correct proxy settings. Now start a
 browser on the device, and visit the magic domain **mitm.it**. You should see
 something like this:
 
-<img src="@!urlTo("certinstall-webapp.png")!@"></img>
+<img class="img-responsive" src="@!urlTo("certinstall-webapp.png")!@" ></img>
 
 Click on the relevant icon, and follow the setup instructions for the platform
 you're on, and you are good to go.