diff --git a/Gemfile b/Gemfile
index 86210e4..798c186 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,4 +1,4 @@
-source :rubygems
+source 'https://rubygems.org'
 
 gemspec
 
diff --git a/features/fixtures/fake_app.rb b/features/fixtures/fake_app.rb
index a13a258..2f58dba 100644
--- a/features/fixtures/fake_app.rb
+++ b/features/fixtures/fake_app.rb
@@ -29,5 +29,10 @@ class FakeApp < Sinatra::Base
       input_data = JSON.parse request.env["rack.input"].read, symbolize_names: true
       status 201 if input_data == {publisher: 'Pragprog'}
     end
+
+    put '/api/publishers/123' do
+      input_data = JSON.parse request.env["rack.input"].read, symbolize_names: true
+      status 200 if input_data == {publisher: 'Pragprog'}
+    end
   end
 end
diff --git a/features/request.feature b/features/request.feature
index 866e7a4..8b4abfd 100644
--- a/features/request.feature
+++ b/features/request.feature
@@ -7,6 +7,21 @@ Feature:
       """
     Then the response status should be "200"
 
+  Scenario: GET request with defined instance variable method referenced from step
+    Given I define instance variable @defined = "BOOKS"
+    When I perform the following step:
+      """
+      I send a GET request to "/api/[@defined.downcase]"
+      """
+    Then the response status should be "200"
+
+  Scenario: GET request with undefined instance variable referenced from step
+    When I perform the following steps which may raise ArgumentError:
+      """
+      I send a GET request to "/api/[@undefined]"
+      """
+    Then ArgumentError was raised
+
   Scenario: POST request with params
     When I perform the following step with table:
       """
@@ -23,3 +38,12 @@ Feature:
       {"publisher": "Pragprog"}
       """
     Then the response status should be "201"
+
+  Scenario: PUT request with defined instance variable method referenced from step
+    Given I define instance variable @publisher = OpenStruct.new(:id => 123)
+    When I perform the following step with string:
+      """
+      I send a PUT request to "/api/publishers/[@publisher.id]" with the following:
+      {"publisher": "Pragprog"}
+      """
+    Then the response status should be "200"
diff --git a/features/step_definitions/api_test_steps.rb b/features/step_definitions/api_test_steps.rb
index 2b477e8..f7ba55e 100644
--- a/features/step_definitions/api_test_steps.rb
+++ b/features/step_definitions/api_test_steps.rb
@@ -1,10 +1,31 @@
 require 'active_support/core_ext'
 
+Given /^I define instance variable (@[\w]+) = (.*)$/ do |name, value|
+  instance_variable_set(name, eval(value))
+end
+
 When /^I perform the following steps?:$/ do |step_strings|
   steps = step_strings.split("\n")
   steps.each {|step_string| step step_string }
 end
 
+When /^I perform the following steps which may raise ([\w]+)?:$/ do |exception_name, step_strings|
+  exception_type = exception_name.constantize
+  steps = step_strings.split("\n")
+  steps.each do |step_string|
+    begin
+      step step_string
+    rescue exception_type => ex
+      @last_exception = ex
+    end
+  end
+end
+
+Then /^([\w]+) was raised$/ do |exception_name|
+  exception_type = exception_name.constantize
+  @last_exception.should be_an_instance_of(exception_type)
+end
+
 Then /^the response should equal:$/ do |response_body|
   last_response.body.should eq(response_body)
 end
diff --git a/lib/cucumber/api_steps.rb b/lib/cucumber/api_steps.rb
index 0e1d496..0a11de9 100644
--- a/lib/cucumber/api_steps.rb
+++ b/lib/cucumber/api_steps.rb
@@ -14,6 +14,21 @@ def to_str
 
 end
 
+module InstanceVarsInStepArguments
+  # @return [String] arg, replacing any '[@ivar.id]' sub strings by the value of @ivar.id
+  def interpolate_step_arg(arg)
+    r = /\[(@[^\]\s]+)\]/
+    arg && arg.gsub(r) do
+      name, field = $1 && $1.split('.')
+      ivar = instance_variable_get(name)
+      raise ArgumentError, "undefined instance variable '#{name}'" unless ivar
+      field ? ivar.send(field) : ivar
+    end
+  end
+end
+
+World(InstanceVarsInStepArguments)
+
 Given /^I set headers:$/ do |headers|
   headers.rows_hash.each {|k,v| header k, v }
 end
@@ -38,7 +53,7 @@ def to_str
 
 When /^I send a (GET|POST|PUT|DELETE) request (?:for|to) "([^"]*)"(?: with the following:)?$/ do |*args|
   request_type = args.shift
-  path = args.shift
+  path = interpolate_step_arg(args.shift)
   input = args.shift
 
   request_opts = {method: request_type.downcase.to_sym}