diff --git a/lib/ship_compliant/client.rb b/lib/ship_compliant/client.rb
index cbceddf..28de487 100644
--- a/lib/ship_compliant/client.rb
+++ b/lib/ship_compliant/client.rb
@@ -3,6 +3,14 @@ class << self
     attr_accessor :ship_compliant_client
   end
 
+  def self.ship_compliant_client
+    Thread.current[:ship_compliant_client]
+  end
+
+  def self.ship_compliant_client=(client)
+    Thread.current[:ship_compliant_client] = client
+  end
+
   # Returns an instance of +Client+.
   def self.client
     self.ship_compliant_client ||= new_client_from_wsdl(configuration.wsdl)
diff --git a/lib/ship_compliant/configuration.rb b/lib/ship_compliant/configuration.rb
index 6e9a7e0..644691f 100644
--- a/lib/ship_compliant/configuration.rb
+++ b/lib/ship_compliant/configuration.rb
@@ -8,7 +8,11 @@ def self.configure
   end
 
   def self.configuration
-    @configuration ||= Configuration.new
+    Thread.current[:ship_compliant_configuration] ||= Configuration.new
+  end
+
+  def self.configuration=(value)
+    Thread.current[:ship_compliant_configuration] = value
   end
 
   # Stores runtime configuration to authenticate user.
diff --git a/lib/ship_compliant/search_sales_orders_result.rb b/lib/ship_compliant/search_sales_orders_result.rb
index 58f041d..70861fd 100644
--- a/lib/ship_compliant/search_sales_orders_result.rb
+++ b/lib/ship_compliant/search_sales_orders_result.rb
@@ -62,9 +62,7 @@ def paging_cookie_expires
     # Standardizes the XML response by converting fields to integers
     # and forcing the order summaries into an array.
     def parse!
-      unless raw.has_key?(:sales_orders)
-        raw[:sales_orders] = {}
-      end
+      raw[:sales_orders] ||= {}
 
       # force orders to be an array
       orders = raw[:sales_orders].fetch(:sales_order_summary, {})
diff --git a/ship_compliant.gemspec b/ship_compliant.gemspec
index ee36cb7..7627a29 100644
--- a/ship_compliant.gemspec
+++ b/ship_compliant.gemspec
@@ -20,10 +20,10 @@ Gem::Specification.new do |s|
   s.test_files    = s.files.grep(%r{^(test|spec|features)/})
   s.require_paths = ["lib"]
 
-  s.add_dependency "activesupport", "~> 4.0", ">= 4.0.3"
+  s.add_dependency "activesupport", ">= 4.0.3"
   s.add_dependency "savon", "~> 2.3"
 
-  s.add_development_dependency "bundler", "~> 1.5"
+  s.add_development_dependency "bundler", "~> 2.0"
   s.add_development_dependency "rake", "~> 10.0"
   s.add_development_dependency "sdoc", "~> 0.4"
   s.add_development_dependency "pry", "~> 0.9"
diff --git a/spec/lib/ship_compliant/client_spec.rb b/spec/lib/ship_compliant/client_spec.rb
index 5e79b11..be4c6d4 100644
--- a/spec/lib/ship_compliant/client_spec.rb
+++ b/spec/lib/ship_compliant/client_spec.rb
@@ -20,6 +20,22 @@ module ShipCompliant
       expect(ShipCompliant.client.globals[:log]).to be_falsey
     end
 
+    it "don't share configuration between threads" do
+      ShipCompliant.configure do |c|
+        c.username = 'foo'
+      end
+
+      Thread.new do
+        ShipCompliant.configure do |c|
+          c.username = 'bar'
+        end
+
+        expect(ShipCompliant.configuration.username).to eq('bar')
+      end.join
+
+      expect(ShipCompliant.configuration.username).to eq('foo')
+    end
+
     context "call" do
       before { savon.mock! }
       after { savon.unmock! }