diff --git a/UPGRADING.md b/UPGRADING.md
index bf362f6a1..8acd82401 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -87,6 +87,7 @@ For more details, see https://github.com/lostisland/faraday/pull/1306
 * Drop `Faraday::UploadIO` in favour of `Faraday::FilePart`.
 * `Faraday.default_connection_options` will now be deep-merged into new connections to avoid overriding them (e.g. headers).
 * Retry middleware `retry_block` is not called if retry will not happen due to `max_interval`. (#1350)
+* `Faraday::Builder#build` method is not exposed through `Faraday::Connection` anymore and does not reset the handlers if called multiple times. This method should be used internally only.
 
 ## Faraday 1.0
 
diff --git a/lib/faraday.rb b/lib/faraday.rb
index 687d70a4d..4b1354087 100644
--- a/lib/faraday.rb
+++ b/lib/faraday.rb
@@ -150,5 +150,4 @@ def method_missing(name, *args, &block)
   self.ignore_env_proxy = false
   self.root_path = File.expand_path __dir__
   self.lib_path = File.expand_path 'faraday', __dir__
-  self.default_adapter = :test
 end
diff --git a/lib/faraday/connection.rb b/lib/faraday/connection.rb
index 20551a749..9dab543ca 100644
--- a/lib/faraday/connection.rb
+++ b/lib/faraday/connection.rb
@@ -117,7 +117,7 @@ def headers=(hash)
 
     extend Forwardable
 
-    def_delegators :builder, :build, :use, :request, :response, :adapter, :app
+    def_delegators :builder, :use, :request, :response, :adapter, :app
 
     # Closes the underlying resources and/or connections. In the case of
     # persistent connections, this closes all currently open connections
diff --git a/lib/faraday/rack_builder.rb b/lib/faraday/rack_builder.rb
index c000d51f9..aa433c10b 100644
--- a/lib/faraday/rack_builder.rb
+++ b/lib/faraday/rack_builder.rb
@@ -58,22 +58,21 @@ def build(app = nil)
       end
     end
 
-    def initialize(handlers = [], adapter = nil, &block)
-      @adapter = adapter
-      @handlers = handlers
-      if block
-        build(&block)
-      elsif @handlers.empty?
-        # default stack, if nothing else is configured
-        request :url_encoded
-        self.adapter Faraday.default_adapter
-      end
+    def initialize(&block)
+      @adapter = nil
+      @handlers = []
+      build(&block)
+    end
+
+    def initialize_dup(original)
+      super
+      @adapter = original.adapter
+      @handlers = original.handlers.dup
     end
 
-    def build(options = {})
+    def build
       raise_if_locked
-      @handlers.clear unless options[:keep]
-      yield(self) if block_given?
+      block_given? ? yield(self) : request(:url_encoded)
       adapter(Faraday.default_adapter) unless @adapter
     end
 
@@ -109,7 +108,7 @@ def locked?
     end
 
     ruby2_keywords def adapter(klass = NO_ARGUMENT, *args, &block)
-      return @adapter if klass == NO_ARGUMENT
+      return @adapter if klass == NO_ARGUMENT || klass.nil?
 
       klass = Faraday::Adapter.lookup_middleware(klass) if klass.is_a?(Symbol)
       @adapter = self.class::Handler.new(klass, *args, &block)
@@ -164,6 +163,7 @@ def build_response(connection, request)
     def app
       @app ||= begin
         lock!
+        ensure_adapter!
         to_app
       end
     end
@@ -182,10 +182,6 @@ def ==(other)
         @adapter == other.adapter
     end
 
-    def dup
-      self.class.new(@handlers.dup, @adapter.dup)
-    end
-
     # ENV Keys
     # :http_method - a symbolized request HTTP method (:get, :post)
     # :body   - the request body that will eventually be converted to a string.
@@ -216,6 +212,9 @@ def build_env(connection, request)
     private
 
     LOCK_ERR = "can't modify middleware stack after making a request"
+    MISSING_ADAPTER_ERROR = "An attempt to run a request with a Faraday::Connection without adapter has been made.\n" \
+                            "Please set Faraday.default_adapter or provide one when initializing the connection.\n" \
+                            'For more info, check https://lostisland.github.io/faraday/usage/.'
 
     def raise_if_locked
       raise StackLocked, LOCK_ERR if locked?
@@ -227,6 +226,10 @@ def raise_if_adapter(klass)
       raise 'Adapter should be set using the `adapter` method, not `use`'
     end
 
+    def ensure_adapter!
+      raise MISSING_ADAPTER_ERROR unless @adapter
+    end
+
     def adapter_set?
       !@adapter.nil?
     end
diff --git a/spec/faraday/connection_spec.rb b/spec/faraday/connection_spec.rb
index 7111a6a7d..fddcac2b9 100644
--- a/spec/faraday/connection_spec.rb
+++ b/spec/faraday/connection_spec.rb
@@ -151,6 +151,9 @@ def decode(params)
   end
 
   describe '#close' do
+    before { Faraday.default_adapter = :test }
+    after { Faraday.default_adapter = nil }
+
     it 'can close underlying app' do
       expect(conn.app).to receive(:close)
       conn.close
diff --git a/spec/faraday/rack_builder_spec.rb b/spec/faraday/rack_builder_spec.rb
index b9a4ef957..6a0a44790 100644
--- a/spec/faraday/rack_builder_spec.rb
+++ b/spec/faraday/rack_builder_spec.rb
@@ -20,6 +20,8 @@ class Banana < Handler
   end
 
   subject { conn.builder }
+  before { Faraday.default_adapter = :test }
+  after { Faraday.default_adapter = nil }
 
   context 'with default stack' do
     let(:conn) { Faraday::Connection.new }
@@ -86,13 +88,6 @@ class Banana < Handler
 
     it { expect(subject.handlers).to eq([Apple]) }
 
-    it 'allows rebuilding' do
-      subject.build do |builder|
-        builder.use(Orange)
-      end
-      expect(subject.handlers).to eq([Orange])
-    end
-
     it 'allows use' do
       subject.use(Orange)
       expect(subject.handlers).to eq([Apple, Orange])