diff --git a/bin/unicorn b/bin/unicorn
index 865e8d87dce..38e238c1f31 100755
--- a/bin/unicorn
+++ b/bin/unicorn
@@ -4,12 +4,35 @@
 require 'pathname'
 ENV['BUNDLE_GEMFILE'] ||= File.expand_path("../../Gemfile",
   Pathname.new(__FILE__).realpath)
+RAILS_ROOT = File.expand_path("../../", Pathname.new(__FILE__).realpath)
 
 require 'rubygems'
 require 'bundler/setup'
+require 'digest'
 
 dev_mode = false
 
+def ensure_cache_clean!
+  all_plugin_directories = Pathname.new(RAILS_ROOT + '/plugins').children.select(&:directory?)
+  core_git_sha = `git rev-parse HEAD`
+  sorted_plugin_shas = all_plugin_directories.map do |plugin_dir|
+    "#{plugin_dir}:" + `git ls-files -s #{plugin_dir} | git hash-object --stdin`
+  end.sort
+  supersha_hash = Digest::SHA1.hexdigest((sorted_plugin_shas + [core_git_sha]).join('|'))
+  hash_file = "#{RAILS_ROOT}/tmp/plugin-hash"
+
+  old_hash = File.exists?(hash_file) ? File.read(hash_file) : nil
+
+  if old_hash && old_hash != supersha_hash
+    puts "WARNING: It looks like your discourse plugins or core version have recently changed."
+    puts "The tmp/cache directory will be wiped to avoid development issues."
+    `rm -rf #{RAILS_ROOT}/tmp/cache`
+    puts
+  end
+
+  File.write(hash_file, supersha_hash)
+end
+
 # in development do some fussing around, to automate config
 if !ARGV.include?("-E") &&
     !ARGV.include?("--env") &&
@@ -38,6 +61,7 @@ if !ARGV.include?("-E") &&
 
   ENV["UNICORN_SIDEKIQS"] ||= "1"
 
+  ensure_cache_clean!
 end
 
 if ARGV.include?("--help")
diff --git a/lib/discourse.rb b/lib/discourse.rb
index 891bc01f07f..c61a2f14e7d 100644
--- a/lib/discourse.rb
+++ b/lib/discourse.rb
@@ -183,29 +183,8 @@ module Discourse
   end
 
   def self.activate_plugins!
-    all_plugins = Plugin::Instance.find_all("#{Rails.root}/plugins")
-
-    if Rails.env.development?
-      plugin_hash = Digest::SHA1.hexdigest(all_plugins.map { |p| p.path }.sort.join('|'))
-      hash_file = "#{Rails.root}/tmp/plugin-hash"
-
-      old_hash = begin
-        File.read(hash_file)
-      rescue Errno::ENOENT
-      end
-
-      if old_hash && old_hash != plugin_hash
-        puts "WARNING: It looks like your discourse plugins have recently changed."
-        puts "It is highly recommended to remove your `tmp` directory, otherwise"
-        puts "plugins might not work."
-        puts
-      else
-        File.write(hash_file, plugin_hash)
-      end
-    end
-
     @plugins = []
-    all_plugins.each do |p|
+    Plugin::Instance.find_all("#{Rails.root}/plugins").each do |p|
       v = p.metadata.required_version || Discourse::VERSION::STRING
       if Discourse.has_needed_version?(Discourse::VERSION::STRING, v)
         p.activate!