diff --git a/lib/open_api_spex/cast.ex b/lib/open_api_spex/cast.ex
index 269cf3f4..ea623d61 100644
--- a/lib/open_api_spex/cast.ex
+++ b/lib/open_api_spex/cast.ex
@@ -119,8 +119,12 @@ defmodule OpenApiSpex.Cast do
   @spec cast(t()) :: {:ok, term()} | {:error, [Error.t()]}
 
   # Custom validator
-  def cast(%__MODULE__{schema: %{"x-validate": module}} = ctx) when module != nil,
-    do: module.cast(ctx)
+  def cast(%__MODULE__{schema: %{"x-validate": module}} = ctx)
+      when is_atom(module) and module != nil,
+      do: module.cast(ctx)
+
+  def cast(%__MODULE__{schema: %{"x-validate": module}} = ctx) when is_binary(module),
+    do: module |> Elixir.String.split(".") |> Module.concat() |> then(& &1.cast(ctx))
 
   # nil schema
   def cast(%__MODULE__{value: value, schema: nil}),
diff --git a/test/cast_test.exs b/test/cast_test.exs
index 09de70df..f0d71273 100644
--- a/test/cast_test.exs
+++ b/test/cast_test.exs
@@ -7,6 +7,23 @@ defmodule OpenApiSpec.CastTest do
   def cast(ctx), do: Cast.cast(ctx)
 
   describe "cast/1" do
+    defmodule CustomValidator.EvenInt do
+      require OpenApiSpex
+
+      alias OpenApiSpex.Cast
+
+      OpenApiSpex.schema(%{
+        description: "An even integer",
+        type: :integer,
+        "x-validate": __MODULE__
+      })
+
+      def cast(context = %Cast{value: value}) when is_integer(value) and rem(value, 2) == 0,
+        do: Cast.ok(context)
+
+      def cast(context), do: Cast.error(context, {:custom, "Must be an even integer"})
+    end
+
     test "unknown schema type" do
       assert {:error, [error]} = cast(value: "string", schema: %Schema{type: :nope})
       assert error.reason == :invalid_schema_type
@@ -223,24 +240,7 @@ defmodule OpenApiSpec.CastTest do
     end
 
     test "cast custom error with custom validator" do
-      defmodule EvenInt do
-        require OpenApiSpex
-
-        alias OpenApiSpex.Cast
-
-        OpenApiSpex.schema(%{
-          description: "An even integer",
-          type: :integer,
-          "x-validate": __MODULE__
-        })
-
-        def cast(context = %Cast{value: value}) when is_integer(value) and rem(value, 2) == 0,
-          do: Cast.ok(context)
-
-        def cast(context), do: Cast.error(context, {:custom, "Must be an even integer"})
-      end
-
-      schema = %Schema{type: :object, properties: %{even_number: EvenInt.schema()}}
+      schema = %Schema{type: :object, properties: %{even_number: CustomValidator.EvenInt.schema()}}
 
       assert {:error, errors} = cast(value: %{"even_number" => 1}, schema: schema)
       assert [error] = errors
@@ -250,6 +250,21 @@ defmodule OpenApiSpec.CastTest do
       assert Error.message_with_path(error) == "#/even_number: Must be an even integer"
     end
 
+    test "cast with custom validator from decoded schema" do
+      spec =
+        "./test/support/encoded_schema.json"
+        |> File.read!()
+        |> Jason.decode!()
+        |> OpenApiSpex.OpenApi.Decode.decode()
+
+      %{
+        components: %{schemas: %{"CustomValidationDecoded" => custom_validation_schema}}
+      } = spec
+
+      assert {:ok, %{even_num: 2}} =
+               cast(value: %{"even_num" => 2}, schema: custom_validation_schema)
+    end
+
     test "nil value with xxxOf" do
       schema = %Schema{anyOf: [%Schema{nullable: true, type: :string}]}
       assert {:ok, nil} = cast(value: nil, schema: schema)
diff --git a/test/support/encoded_schema.json b/test/support/encoded_schema.json
index 7d77ea03..a7992696 100644
--- a/test/support/encoded_schema.json
+++ b/test/support/encoded_schema.json
@@ -280,6 +280,15 @@
         "not": {
           "type": "string"
         }
+      },
+      "CustomValidationDecoded": {
+        "type": "object",
+        "properties": {
+          "even_num": {
+            "type": "integer",
+            "x-validate": "OpenApiSpec.CastTest.CustomValidator.EvenInt"
+          }
+        }
       }
     },
     "links": {