diff --git a/README.md b/README.md
index 85d3f80..5a8d334 100644
--- a/README.md
+++ b/README.md
@@ -161,8 +161,11 @@ makes debugging easier). Running `rake autocompile` will watch the
     `getBoundingClientRect()` method, which will be faster and less
     buggy.
 
-*   Handle `window.confirm()`. (Always returns true, which is the same
-    as capybara-webkit.) [Issue #10]
+*   Handle `window.confirm()`. Always returns true, which is the same
+    as capybara-webkit. [Issue #10]
+
+*   Handle `window.prompt()`. Returns the default value, if present, or
+    null.
 
 ### 0.3.0 ###
 
diff --git a/lib/capybara/poltergeist/client/agent.coffee b/lib/capybara/poltergeist/client/agent.coffee
index 5c6f264..24f644e 100644
--- a/lib/capybara/poltergeist/client/agent.coffee
+++ b/lib/capybara/poltergeist/client/agent.coffee
@@ -177,3 +177,4 @@ document.addEventListener(
 )
 
 window.confirm = (message) -> true
+window.prompt  = (message, _default) -> _default or null
diff --git a/lib/capybara/poltergeist/client/compiled/agent.js b/lib/capybara/poltergeist/client/compiled/agent.js
index e27cdb9..bb7a104 100644
--- a/lib/capybara/poltergeist/client/compiled/agent.js
+++ b/lib/capybara/poltergeist/client/compiled/agent.js
@@ -205,4 +205,7 @@ document.addEventListener('DOMContentLoaded', function() {
 });
 window.confirm = function(message) {
   return true;
+};
+window.prompt = function(message, _default) {
+  return _default || null;
 };
\ No newline at end of file
diff --git a/spec/integration/session_spec.rb b/spec/integration/session_spec.rb
index 214748d..6c7ac7b 100644
--- a/spec/integration/session_spec.rb
+++ b/spec/integration/session_spec.rb
@@ -75,9 +75,15 @@ describe Capybara::Session do
       end
     end
 
-    it 'should handle window.confirm() - returning true unconditionally' do
+    it 'should handle window.confirm(), returning true unconditionally' do
       @session.visit '/'
       @session.evaluate_script("window.confirm('foo')").should == true
     end
+
+    it 'should handle window.prompt(), returning the default value or null' do
+      @session.visit '/'
+      @session.evaluate_script("window.prompt()").should == nil
+      @session.evaluate_script("window.prompt('foo', 'default')").should == 'default'
+    end
   end
 end