diff --git a/lib/prometheus/client/histogram.rb b/lib/prometheus/client/histogram.rb
index 12d1ed78..97504543 100644
--- a/lib/prometheus/client/histogram.rb
+++ b/lib/prometheus/client/histogram.rb
@@ -42,12 +42,18 @@ def self.exponential_buckets(start:, factor: 2, count:)
       end
 
       def with_labels(labels)
-        self.class.new(name,
-                       docstring: docstring,
-                       labels: @labels,
-                       preset_labels: preset_labels.merge(labels),
-                       buckets: @buckets,
-                       store_settings: @store_settings)
+        new_metric = self.class.new(name,
+                                    docstring: docstring,
+                                    labels: @labels,
+                                    preset_labels: preset_labels.merge(labels),
+                                    buckets: @buckets,
+                                    store_settings: @store_settings)
+
+        # The new metric needs to use the same store as the "main" declared one, otherwise
+        # any observations on that copy with the pre-set labels won't actually be exported.
+        new_metric.replace_internal_store(@store)
+
+        new_metric
       end
 
       def type
diff --git a/lib/prometheus/client/metric.rb b/lib/prometheus/client/metric.rb
index 100e455b..899926e6 100644
--- a/lib/prometheus/client/metric.rb
+++ b/lib/prometheus/client/metric.rb
@@ -40,8 +40,16 @@ def initialize(name,
           metric_type: type,
           metric_settings: store_settings
         )
+
+        # WARNING: Our internal store can be replaced later by `with_labels`
+        # Everything we do after this point needs to still work if @store gets replaced
+      end
+
+      protected def replace_internal_store(new_store)
+        @store = new_store
       end
 
+
       # Returns the value for the given label set
       def get(labels: {})
         label_set = label_set_for(labels)
@@ -49,11 +57,17 @@ def get(labels: {})
       end
 
       def with_labels(labels)
-        self.class.new(name,
-                       docstring: docstring,
-                       labels: @labels,
-                       preset_labels: preset_labels.merge(labels),
-                       store_settings: @store_settings)
+        new_metric = self.class.new(name,
+                                     docstring: docstring,
+                                     labels: @labels,
+                                     preset_labels: preset_labels.merge(labels),
+                                     store_settings: @store_settings)
+
+        # The new metric needs to use the same store as the "main" declared one, otherwise
+        # any observations on that copy with the pre-set labels won't actually be exported.
+        new_metric.replace_internal_store(@store)
+
+        new_metric
       end
 
       def init_label_set(labels)
diff --git a/lib/prometheus/client/push.rb b/lib/prometheus/client/push.rb
index 03efb9f7..3078811a 100644
--- a/lib/prometheus/client/push.rb
+++ b/lib/prometheus/client/push.rb
@@ -3,6 +3,7 @@
 require 'thread'
 require 'net/http'
 require 'uri'
+require 'cgi'
 
 require 'prometheus/client'
 require 'prometheus/client/formats/text'
@@ -20,7 +21,7 @@ class Push
 
       attr_reader :job, :instance, :gateway, :path
 
-      def initialize(job, instance = nil, gateway = nil)
+      def initialize(job, instance = nil, gateway = nil, **kwargs)
         @mutex = Mutex.new
         @job = job
         @instance = instance
@@ -30,6 +31,8 @@ def initialize(job, instance = nil, gateway = nil)
 
         @http = Net::HTTP.new(@uri.host, @uri.port)
         @http.use_ssl = (@uri.scheme == 'https')
+        @http.open_timeout = kwargs[:open_timeout] if kwargs[:open_timeout]
+        @http.read_timeout = kwargs[:read_timeout] if kwargs[:read_timeout]
       end
 
       def add(registry)
diff --git a/lib/prometheus/client/registry.rb b/lib/prometheus/client/registry.rb
index 4bf63aa4..0b2f6e9a 100644
--- a/lib/prometheus/client/registry.rb
+++ b/lib/prometheus/client/registry.rb
@@ -22,7 +22,7 @@ def register(metric)
         name = metric.name
 
         @mutex.synchronize do
-          if exist?(name.to_sym)
+          if @metrics.key?(name.to_sym)
             raise AlreadyRegisteredError, "#{name} has already been registered"
           end
           @metrics[name.to_sym] = metric
@@ -73,15 +73,15 @@ def histogram(name, docstring:, labels: [], preset_labels: {},
       end
 
       def exist?(name)
-        @metrics.key?(name)
+        @mutex.synchronize { @metrics.key?(name) }
       end
 
       def get(name)
-        @metrics[name.to_sym]
+        @mutex.synchronize { @metrics[name.to_sym] }
       end
 
       def metrics
-        @metrics.values
+        @mutex.synchronize { @metrics.values }
       end
     end
   end
diff --git a/lib/prometheus/client/version.rb b/lib/prometheus/client/version.rb
index ec33bff5..0e0f5c54 100644
--- a/lib/prometheus/client/version.rb
+++ b/lib/prometheus/client/version.rb
@@ -2,6 +2,6 @@
 
 module Prometheus
   module Client
-    VERSION = '2.1.0'
+    VERSION = '2.2.0'
   end
 end
diff --git a/lib/prometheus/middleware/exporter.rb b/lib/prometheus/middleware/exporter.rb
index 5a74d8e9..640a3985 100644
--- a/lib/prometheus/middleware/exporter.rb
+++ b/lib/prometheus/middleware/exporter.rb
@@ -21,11 +21,12 @@ def initialize(app, options = {})
         @app = app
         @registry = options[:registry] || Client.registry
         @path = options[:path] || '/metrics'
+        @port = options[:port]
         @acceptable = build_dictionary(FORMATS, FALLBACK)
       end
 
       def call(env)
-        if env['PATH_INFO'] == @path
+        if metrics_port?(env['SERVER_PORT']) && env['PATH_INFO'] == @path
           format = negotiate(env, @acceptable)
           format ? respond_with(format) : not_acceptable(FORMATS)
         else
@@ -86,6 +87,10 @@ def build_dictionary(formats, fallback)
           memo[format::MEDIA_TYPE] = format
         end
       end
+
+      def metrics_port?(request_port)
+        @port.nil? || @port.to_s == request_port
+      end
     end
   end
 end
diff --git a/prometheus-client.gemspec b/prometheus-client.gemspec
index 20ad18bf..21690fab 100644
--- a/prometheus-client.gemspec
+++ b/prometheus-client.gemspec
@@ -8,7 +8,7 @@ Gem::Specification.new do |s|
   s.summary           = 'A suite of instrumentation metric primitives' \
                         'that can be exposed through a web services interface.'
   s.authors           = ['Ben Kochie', 'Chris Sinjakli', 'Daniel Magliola']
-  s.email             = ['superq@gmail.com', 'chris@gocardless.com', 'dmagliola@crystalgears.com']
+  s.email             = ['superq@gmail.com', 'chris@sinjakli.co.uk', 'dmagliola@crystalgears.com']
   s.homepage          = 'https://github.com/prometheus/client_ruby'
   s.license           = 'Apache 2.0'
 
diff --git a/spec/prometheus/client/registry_spec.rb b/spec/prometheus/client/registry_spec.rb
index 32727d00..3c4da190 100644
--- a/spec/prometheus/client/registry_spec.rb
+++ b/spec/prometheus/client/registry_spec.rb
@@ -33,10 +33,6 @@
       mutex = Mutex.new
       containers = []
 
-      def registry.exist?(*args)
-        super.tap { sleep(0.01) }
-      end
-
       Array.new(5) do
         Thread.new do
           result = begin
diff --git a/spec/prometheus/middleware/exporter_spec.rb b/spec/prometheus/middleware/exporter_spec.rb
index 8916513b..5299fc1e 100644
--- a/spec/prometheus/middleware/exporter_spec.rb
+++ b/spec/prometheus/middleware/exporter_spec.rb
@@ -6,13 +6,14 @@
 describe Prometheus::Middleware::Exporter do
   include Rack::Test::Methods
 
+  let(:options) { { registry: registry } }
   let(:registry) do
     Prometheus::Client::Registry.new
   end
 
   let(:app) do
     app = ->(_) { [200, { 'Content-Type' => 'text/html' }, ['OK']] }
-    described_class.new(app, registry: registry)
+    described_class.new(app, **options)
   end
 
   context 'when requesting app endpoints' do
@@ -96,5 +97,30 @@
 
       include_examples 'ok', { 'HTTP_ACCEPT' => accept }, text
     end
+
+    context 'when a port is specified' do
+      let(:options) { { registry: registry, port: 9999 } }
+
+      context 'when a request is on the specified port' do
+        it 'responds with 200 OK' do
+          registry.counter(:foo, docstring: 'foo counter').increment(by: 9)
+
+          get 'http://example.org:9999/metrics', nil, {}
+
+          expect(last_response.status).to eql(200)
+          expect(last_response.header['Content-Type']).to eql(text::CONTENT_TYPE)
+          expect(last_response.body).to eql(text.marshal(registry))
+        end
+      end
+
+      context 'when a request is not on the specified port' do
+        it 'returns the app response' do
+          get 'http://example.org:8888/metrics', nil, {}
+
+          expect(last_response).to be_ok
+          expect(last_response.body).to eql('OK')
+        end
+      end
+    end
   end
 end