diff --git a/lib/puma/rack/builder.rb b/lib/puma/rack/builder.rb
index 88789f74..1ee8f1ac 100644
--- a/lib/puma/rack/builder.rb
+++ b/lib/puma/rack/builder.rb
@@ -290,6 +290,8 @@ module Puma::Rack
     private
 
     def generate_map(default_app, mapping)
+      require 'puma/rack/urlmap'
+
       mapped = default_app ? {'/' => default_app} : {}
       mapping.each { |r,b| mapped[r] = self.class.new(default_app, &b).to_app }
       URLMap.new(mapped)
diff --git a/lib/puma/rack/urlmap.rb b/lib/puma/rack/urlmap.rb
new file mode 100644
index 00000000..a82c7ee8
--- /dev/null
+++ b/lib/puma/rack/urlmap.rb
@@ -0,0 +1,90 @@
+module Puma::Rack
+  # Rack::URLMap takes a hash mapping urls or paths to apps, and
+  # dispatches accordingly.  Support for HTTP/1.1 host names exists if
+  # the URLs start with <tt>http://</tt> or <tt>https://</tt>.
+  #
+  # URLMap modifies the SCRIPT_NAME and PATH_INFO such that the part
+  # relevant for dispatch is in the SCRIPT_NAME, and the rest in the
+  # PATH_INFO.  This should be taken care of when you need to
+  # reconstruct the URL in order to create links.
+  #
+  # URLMap dispatches in such a way that the longest paths are tried
+  # first, since they are most specific.
+
+  class URLMap
+    NEGATIVE_INFINITY = -1.0 / 0.0
+    INFINITY = 1.0 / 0.0
+
+    def initialize(map = {})
+      remap(map)
+    end
+
+    def remap(map)
+      @mapping = map.map { |location, app|
+        if location =~ %r{\Ahttps?://(.*?)(/.*)}
+          host, location = $1, $2
+        else
+          host = nil
+        end
+
+        unless location[0] == ?/
+          raise ArgumentError, "paths need to start with /"
+        end
+
+        location = location.chomp('/')
+        match = Regexp.new("^#{Regexp.quote(location).gsub('/', '/+')}(.*)", nil, 'n')
+
+        [host, location, match, app]
+      }.sort_by do |(host, location, _, _)|
+        [host ? -host.size : INFINITY, -location.size]
+      end
+    end
+
+    def call(env)
+      path = env['PATH_INFO']
+      script_name = env['SCRIPT_NAME']
+      hHost = env['HTTP_HOST']
+      sName = env['SERVER_NAME']
+      sPort = env['SERVER_PORT']
+
+      @mapping.each do |host, location, match, app|
+        unless casecmp?(hHost, host) \
+            || casecmp?(sName, host) \
+            || (!host && (casecmp?(hHost, sName) ||
+                          casecmp?(hHost, sName+':'+sPort)))
+          next
+        end
+
+        next unless m = match.match(path.to_s)
+
+        rest = m[1]
+        next unless !rest || rest.empty? || rest[0] == ?/
+
+        env['SCRIPT_NAME'] = (script_name + location)
+        env['PATH_INFO'] = rest
+
+        return app.call(env)
+      end
+
+      [404, {'Content-Type' => "text/plain", "X-Cascade" => "pass"}, ["Not Found: #{path}"]]
+
+    ensure
+      env['PATH_INFO'] = path
+      env['SCRIPT_NAME'] = script_name
+    end
+
+    private
+    def casecmp?(v1, v2)
+      # if both nil, or they're the same string
+      return true if v1 == v2
+
+      # if either are nil... (but they're not the same)
+      return false if v1.nil?
+      return false if v2.nil?
+
+      # otherwise check they're not case-insensitive the same
+      v1.casecmp(v2).zero?
+    end
+  end
+end
+
diff --git a/test/hello-map.ru b/test/hello-map.ru
new file mode 100644
index 00000000..11401d48
--- /dev/null
+++ b/test/hello-map.ru
@@ -0,0 +1,3 @@
+map "/foo" do
+  run lambda { |env| [200, {"Content-Type" => "text/plain"}, ["Hello World"]] }
+end