diff --git a/config/config.exs b/config/config.exs
index 08f7580..475234a 100644
--- a/config/config.exs
+++ b/config/config.exs
@@ -1,6 +1,6 @@
 # This file is responsible for configuring your application
 # and its dependencies with the aid of the Mix.Config module.
-use Mix.Config
+import Config
 
 # This configuration is loaded before any dependency and is restricted
 # to this project. If another project depends on this project, this
diff --git a/config/dev.exs b/config/dev.exs
index d2d855e..b30c7d0 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -1 +1 @@
-use Mix.Config
+use Config
diff --git a/config/test.exs b/config/test.exs
index 678a891..1265799 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -1,4 +1,4 @@
-use Mix.Config
+import Config
 
 defmodule CustomFormatValidator do
   def validate(_format, _data), do: true
diff --git a/lib/ex_json_schema/validator/format.ex b/lib/ex_json_schema/validator/format.ex
index 92bd24d..730a3cf 100644
--- a/lib/ex_json_schema/validator/format.ex
+++ b/lib/ex_json_schema/validator/format.ex
@@ -111,6 +111,7 @@ defmodule ExJsonSchema.Validator.Format do
     case apply(mod, fun, [format, data]) do
       true -> []
       false -> [%Error{error: %Error.Format{expected: format}}]
+      {false, custom_validation_error_format_name} -> [%Error{error: %Error.Format{expected: custom_validation_error_format_name}}]
     end
   end
 end
diff --git a/test/ex_json_schema/schema_test.exs b/test/ex_json_schema/schema_test.exs
index d28569e..526c262 100644
--- a/test/ex_json_schema/schema_test.exs
+++ b/test/ex_json_schema/schema_test.exs
@@ -35,7 +35,7 @@ defmodule ExJsonSchema.SchemaTest do
     schema = %{"properties" => "foo"}
 
     assert_raise ExJsonSchema.Schema.InvalidSchemaError,
-                 ~s(schema did not pass validation against its meta-schema: [%ExJsonSchema.Validator.Error{error: %ExJsonSchema.Validator.Error.Type{actual: "string", expected: ["object"]}, path: "#/properties"}]),
+                 ~s(schema did not pass validation against its meta-schema: [%ExJsonSchema.Validator.Error{error: %ExJsonSchema.Validator.Error.Type{expected: ["object"], actual: "string"}, path: "#/properties"}]),
                  fn -> resolve(schema) end
   end
 
diff --git a/test/ex_json_schema/validator_test.exs b/test/ex_json_schema/validator_test.exs
index 7b4d71c..1f7948a 100644
--- a/test/ex_json_schema/validator_test.exs
+++ b/test/ex_json_schema/validator_test.exs
@@ -723,6 +723,10 @@ defmodule ExJsonSchema.ValidatorTest do
       false
     end
 
+    def validate("custom_validation_error_format_name", _data) do
+      {false, "custom_format_fieldname"}
+    end
+
     def validate("zipcode", data) do
       Regex.match?(~r/^\d+$/, data)
     end
@@ -757,6 +761,25 @@ defmodule ExJsonSchema.ValidatorTest do
     )
   end
 
+  test "configuring a custom format validator with custom error message" do
+    schema =
+      Schema.resolve(
+        %{
+          "properties" => %{
+            "error" => %{"format" => "custom_validation_error_format_name"}
+          }
+        },
+        custom_format_validator: {MyFormatValidator, :validate}
+      )
+
+    assert_validation_errors(
+      schema,
+      %{"error" => ""},
+      [{"Expected to be a valid custom_format_fieldname.", "#/error"}],
+      [%Error{error: %Error.Format{expected: "custom_format_fieldname"}, path: "#/error"}]
+    )
+  end
+
   test "passing the formatter as an option" do
     assert :ok = validate(%{"type" => "string"}, "foo", error_formatter: Error.StringFormatter)