diff --git a/CHANGELOG.md b/CHANGELOG.md
index a01f78e..800e455 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,8 +2,10 @@
 
 ## Unreleased
 
-## 1.22.0
 
+- [#400](https://github.com/JsonApiClient/json_api_client/pull/400) - Fix for multi-word custom endpoint and route format
+
+## 1.22.0
 - [#403](https://github.com/JsonApiClient/json_api_client/pull/403) - Feature: Use the association options to lookup relationship class
 - [#406](https://github.com/JsonApiClient/json_api_client/pull/406) - Deep-merge nested `additional_params`
 
diff --git a/lib/json_api_client/resource.rb b/lib/json_api_client/resource.rb
index 0665c99..4ef7313 100644
--- a/lib/json_api_client/resource.rb
+++ b/lib/json_api_client/resource.rb
@@ -260,10 +260,11 @@ def collection_endpoint(name, options = {})
         metaclass = class << self
           self
         end
+        endpoint_name = _name_for_route_format(name)
         metaclass.instance_eval do
           define_method(name) do |*params|
             request_params = params.first || {}
-            requestor.custom(name, options, request_params)
+            requestor.custom(endpoint_name, options, request_params)
           end
         end
       end
@@ -274,10 +275,11 @@ def collection_endpoint(name, options = {})
       # @param options [Hash] endpoint options
       # @option options [Symbol] :request_method The request method (:get, :post, etc)
       def member_endpoint(name, options = {})
+        endpoint_name = self._name_for_route_format(name)
         define_method name do |*params|
           request_params = params.first || {}
           request_params[self.class.primary_key] = attributes.fetch(self.class.primary_key)
-          self.class.requestor.custom(name, options, request_params)
+          self.class.requestor.custom(endpoint_name, options, request_params)
         end
       end
 
@@ -348,6 +350,17 @@ def _build_connection(rebuild = false)
           yield(conn) if block_given?
         end
       end
+
+      def _name_for_route_format(name)
+        case self.route_format
+        when :dasherized_route
+          name.to_s.dasherize
+        when :camelized_route
+          name.to_s.camelize(:lower)
+        else
+          name
+        end
+      end
     end
 
     # Instantiate a new resource object
diff --git a/test/unit/custom_endpoint_test.rb b/test/unit/custom_endpoint_test.rb
index 017757d..e260f4d 100644
--- a/test/unit/custom_endpoint_test.rb
+++ b/test/unit/custom_endpoint_test.rb
@@ -7,6 +7,24 @@ class Country < TestResource
 
 end
 
+class Pet < TestResource
+  self.site = "http://example.com/"
+  self.route_format = :dasherized_route
+
+  custom_endpoint :related_pets, on: :member, request_method: :get
+  custom_endpoint :vip_pets, on: :collection, request_method: :get
+
+end
+
+class MythicBeasts < TestResource
+  self.site = "http://example.com/"
+  self.route_format = :camelized_route
+
+  custom_endpoint :related_beasts, on: :member, request_method: :get
+  custom_endpoint :ancient_beasts, on: :collection, request_method: :get
+
+end
+
 class CustomEndpointTest < Minitest::Test
 
   def test_collection_get
@@ -43,4 +61,72 @@ def test_collection_methods_should_not_add_methods_to_all_classes
     assert !Class.respond_to?(:autocomplete), "adding a custom method should not add methods to all classes"
   end
 
+  def test_member_dasherized_route_format_converts_custom_endpoint
+    stub_request(:get, "http://example.com/pets/1/related-pets")
+      .to_return(headers: {content_type: "application/vnd.api+json"}, body: {
+        data: [
+          {id: 1, type: 'pets'},
+          {id: 2, type: 'pets'},
+        ]
+      }.to_json)
+
+    pet = Pet.new({id: 1, name: 'Otto'})
+    pet.mark_as_persisted!
+
+    related_pets = pet.related_pets
+
+    assert_equal 2, related_pets.length
+    assert_equal [1,2], related_pets.map(&:id)
+  end
+
+  def test_collection_dasherized_route_format_converts_custom_endpoint
+    stub_request(:get, "http://example.com/pets/vip-pets")
+      .to_return(headers: {content_type: "application/vnd.api+json"}, body: {
+        data: [
+          {id: 4, type: 'pets'},
+          {id: 5, type: 'pets'},
+          {id: 6, type: 'pets'}
+        ]
+      }.to_json)
+
+      vip_pets = Pet.vip_pets
+
+      assert_equal 3, vip_pets.length
+      assert_equal [4,5,6], vip_pets.map(&:id)
+  end
+
+  def test_member_camelized_route_format_converts_custom_endpoint
+    stub_request(:get, "http://example.com/mythicBeasts/1/relatedBeasts")
+      .to_return(headers: {content_type: "application/vnd.api+json"}, body: {
+        data: [
+          {id: 1, type: 'mythic-beasts'},
+          {id: 2, type: 'mythic-beasts'},
+        ]
+      }.to_json)
+
+    dragon = MythicBeasts.new({id: 1, name: 'Dragon'})
+    dragon.mark_as_persisted!
+
+    related_beasts = dragon.related_beasts
+
+    assert_equal 2, related_beasts.length
+    assert_equal [1,2], related_beasts.map(&:id)
+  end
+
+  def test_collection_camelized_route_format_converts_custom_endpoint
+    stub_request(:get, "http://example.com/mythicBeasts/ancientBeasts")
+      .to_return(headers: {content_type: "application/vnd.api+json"}, body: {
+        data: [
+          {id: 4, type: 'mythic-beasts'},
+          {id: 5, type: 'mythic-beasts'},
+          {id: 6, type: 'mythic-beasts'}
+        ]
+      }.to_json)
+
+      ancient_beasts = MythicBeasts.ancient_beasts
+
+      assert_equal 3, ancient_beasts.length
+      assert_equal [4,5,6], ancient_beasts.map(&:id)
+  end
+
 end