diff --git a/.rubocop_todo.yml b/.rubocop_todo.yml
index f62a728f1..4ae11c295 100644
--- a/.rubocop_todo.yml
+++ b/.rubocop_todo.yml
@@ -13,12 +13,12 @@ Metrics/AbcSize:
 # Offense count: 27
 # Configuration parameters: CountComments, ExcludedMethods.
 Metrics/BlockLength:
-  Max: 455
+  Max: 467
 
 # Offense count: 8
 # Configuration parameters: CountComments.
 Metrics/ClassLength:
-  Max: 583
+  Max: 595
 
 # Offense count: 10
 Metrics/CyclomaticComplexity:
diff --git a/lib/stripe/errors.rb b/lib/stripe/errors.rb
index 14081bc15..9d20c3444 100644
--- a/lib/stripe/errors.rb
+++ b/lib/stripe/errors.rb
@@ -66,6 +66,11 @@ def initialize(message, param, code, http_status: nil, http_body: nil, json_body
     end
   end
 
+  # IdempotencyError is raised in cases where an idempotency key was used
+  # improperly.
+  class IdempotencyError < StripeError
+  end
+
   # InvalidRequestError is raised when a request is initiated with invalid
   # parameters.
   class InvalidRequestError < StripeError
diff --git a/lib/stripe/stripe_client.rb b/lib/stripe/stripe_client.rb
index 1434d7fa9..30355da08 100644
--- a/lib/stripe/stripe_client.rb
+++ b/lib/stripe/stripe_client.rb
@@ -280,53 +280,47 @@ def handle_error_response(http_resp, context)
     def specific_api_error(resp, error_data, context)
       Util.log_error("Stripe API error",
                      status: resp.http_status,
-                     error_code: error_data["code"],
-                     error_message: error_data["message"],
-                     error_param: error_data["param"],
-                     error_type: error_data["type"],
+                     error_code: error_data[:code],
+                     error_message: error_data[:message],
+                     error_param: error_data[:param],
+                     error_type: error_data[:type],
                      idempotency_key: context.idempotency_key,
                      request_id: context.request_id)
 
+      # The standard set of arguments that can be used to initialize most of
+      # the exceptions.
+      opts = {
+        http_body: resp.http_body,
+        http_headers: resp.http_headers,
+        http_status: resp.http_status,
+        json_body: resp.data,
+      }
+
       case resp.http_status
       when 400, 404
-        error = InvalidRequestError.new(
-          error_data[:message], error_data[:param],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
-        )
+        case error_data[:type]
+        when "idempotency_error"
+          IdempotencyError.new(error_data[:message], opts)
+        else
+          InvalidRequestError.new(
+            error_data[:message], error_data[:param],
+            opts
+          )
+        end
       when 401
-        error = AuthenticationError.new(
-          error_data[:message],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
-        )
+        AuthenticationError.new(error_data[:message], opts)
       when 402
-        error = CardError.new(
+        CardError.new(
           error_data[:message], error_data[:param], error_data[:code],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
+          opts
         )
       when 403
-        error = PermissionError.new(
-          error_data[:message],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
-        )
+        PermissionError.new(error_data[:message], opts)
       when 429
-        error = RateLimitError.new(
-          error_data[:message],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
-        )
+        RateLimitError.new(error_data[:message], opts)
       else
-        error = APIError.new(
-          error_data[:message],
-          http_status: resp.http_status, http_body: resp.http_body,
-          json_body: resp.data, http_headers: resp.http_headers
-        )
+        APIError.new(error_data[:message], opts)
       end
-
-      error
     end
 
     # Attempts to look at a response's error code and return an OAuth error if
diff --git a/test/stripe/stripe_client_test.rb b/test/stripe/stripe_client_test.rb
index 9c17a8fdd..f78bd8ac9 100644
--- a/test/stripe/stripe_client_test.rb
+++ b/test/stripe/stripe_client_test.rb
@@ -242,10 +242,10 @@ class StripeClientTest < Test::Unit::TestCase
           }
           Util.expects(:log_error).with("Stripe API error",
                                         status: 500,
-                                        error_code: error["code"],
-                                        error_message: error["message"],
-                                        error_param: error["param"],
-                                        error_type: error["type"],
+                                        error_code: error[:code],
+                                        error_message: error[:message],
+                                        error_param: error[:param],
+                                        error_type: error[:type],
                                         idempotency_key: nil,
                                         request_id: nil)
 
@@ -411,7 +411,22 @@ class StripeClientTest < Test::Unit::TestCase
           assert_equal 'Invalid response object from API: "{\"bar\":\"foo\"}" (HTTP response code was 500)', e.message
         end
 
-        should "raise InvalidRequestError on 400" do
+        should "raise IdempotencyError on 400 of type idempotency_error" do
+          data = make_missing_id_error
+          data[:error][:type] = "idempotency_error"
+
+          stub_request(:post, "#{Stripe.api_base}/v1/charges")
+            .to_return(body: JSON.generate(data), status: 400)
+          client = StripeClient.new
+
+          e = assert_raises Stripe::IdempotencyError do
+            client.execute_request(:post, "/v1/charges")
+          end
+          assert_equal(400, e.http_status)
+          assert_equal(true, e.json_body.is_a?(Hash))
+        end
+
+        should "raise InvalidRequestError on other 400s" do
           stub_request(:post, "#{Stripe.api_base}/v1/charges")
             .to_return(body: JSON.generate(make_missing_id_error), status: 400)
           client = StripeClient.new