diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index d74816990b..99a6d6fb48 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -11,6 +11,9 @@ XModule: Don't delete generated xmodule asset files when compiling (for
 instance, when XModule provides a coffeescript file, don't delete
 the associated javascript)
 
+Common: Make asset watchers run as singletons (so they won't start if the
+watcher is already running in another shell).
+
 Common: Make rake provide better error messages if packages are missing.
 
 Common: Repairs development documentation generation by sphinx.
diff --git a/Gemfile b/Gemfile
index 7f7b146978..1ad685c34d 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,3 +4,4 @@ gem 'sass', '3.1.15'
 gem 'bourbon', '~> 1.3.6'
 gem 'colorize', '~> 0.5.8'
 gem 'launchy', '~> 2.1.2'
+gem 'sys-proctable', '~> 0.9.3'
diff --git a/rakelib/assets.rake b/rakelib/assets.rake
index c80b275c27..fbbfdbef7f 100644
--- a/rakelib/assets.rake
+++ b/rakelib/assets.rake
@@ -114,9 +114,9 @@ namespace :assets do
             task :_watch => (prereq_tasks + ["assets:#{asset_type}:debug"]) do
                 cmd = send(asset_type.to_s + "_cmd", watch=true, debug=true)
                 if cmd.kind_of?(Array)
-                    cmd.each {|c| background_process(c)}
+                    cmd.each {|c| singleton_process(c)}
                 else
-                    background_process(cmd)
+                    singleton_process(cmd)
                 end
             end
         end
diff --git a/rakelib/helpers.rb b/rakelib/helpers.rb
index 4b10bef709..3373214a19 100644
--- a/rakelib/helpers.rb
+++ b/rakelib/helpers.rb
@@ -1,4 +1,6 @@
 require 'digest/md5'
+require 'sys/proctable'
+require 'colorize'
 
 def find_executable(exec)
     path = %x(which #{exec}).strip
@@ -84,6 +86,16 @@ def background_process(*command)
     end
 end
 
+# Runs a command as a background process, as long as no other processes
+# tagged with the same tag are running
+def singleton_process(*command)
+    if Sys::ProcTable.ps.select {|proc| proc.cmdline.include?(command.join(' '))}.empty?
+        background_process(*command)
+    else
+        puts "Process '#{command.join(' ')} already running, skipping".blue
+    end
+end
+
 def environments(system)
     Dir["#{system}/envs/**/*.py"].select{|file| ! (/__init__.py$/ =~ file)}.map do |env_file|
         env_file.gsub("#{system}/envs/", '').gsub(/\.py/, '').gsub('/', '.')