diff --git a/CHANGELOG.md b/CHANGELOG.md
index 730d9edb4..d70dc049f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,8 @@
   - Chef-solo provisioner now supports encrypted data bags. [GH-816]
   - Enable the NAT DNS proxy by default, allowing your DNS to continue
     working when you switch networks. [GH-834]
+  - Checking for port forwarding collisions also checks for other applications
+    that are potentially listening on that port as well. [GH-821]
 
 ## 1.0.1 (March 11, 2012)
 
diff --git a/lib/vagrant/action/vm/check_port_collisions.rb b/lib/vagrant/action/vm/check_port_collisions.rb
index 3bb46d80e..254b351ad 100644
--- a/lib/vagrant/action/vm/check_port_collisions.rb
+++ b/lib/vagrant/action/vm/check_port_collisions.rb
@@ -1,9 +1,13 @@
+require "vagrant/util/is_port_open"
+
 module Vagrant
   module Action
     module VM
       # Action that checks to make sure there are no forwarded port collisions,
       # and raises an exception if there is.
       class CheckPortCollisions
+        include Util::IsPortOpen
+
         def initialize(app, env)
           @app = app
         end
@@ -29,7 +33,7 @@ module Vagrant
             hostport = options[:hostport].to_i
             hostport = current[options[:name]] if current.has_key?(options[:name])
 
-            if existing.include?(hostport)
+            if existing.include?(hostport) || is_port_open?("localhost", hostport)
               # We have a collision! Handle it
               send("handle_#{handler}".to_sym, options, existing)
             end