diff --git a/lib/active_model/entity/schemas/json.rb b/lib/active_model/entity/schemas/json.rb
index c6dc7cf..b4af63e 100644
--- a/lib/active_model/entity/schemas/json.rb
+++ b/lib/active_model/entity/schemas/json.rb
@@ -72,6 +72,8 @@ def json_schema_attribute_for(type, inline: false)
           end
 
           def make_schema_nullable!(options)
+            options[:allOf] = ["$ref": options.delete(:$ref)] if options[:$ref].present?
+
             options[:nullable] = true
           end
 
diff --git a/spec/active_model/entity/schemas/json_spec.rb b/spec/active_model/entity/schemas/json_spec.rb
index b037e98..f9a8121 100644
--- a/spec/active_model/entity/schemas/json_spec.rb
+++ b/spec/active_model/entity/schemas/json_spec.rb
@@ -54,8 +54,8 @@ class Person
                    "fieldString" => { type: :string },
                    "fieldTime" => { type: :string },
                    "fieldRole" => { :$ref => "#/components/schemas/SchemasTest.Role" },
-                   "fieldNullableRole" => { :$ref => "#/components/schemas/SchemasTest.Role", nullable: true },
-                   "fieldNullableNotRequiredRole" => { :$ref => "#/components/schemas/SchemasTest.Role", nullable: true },
+                   "fieldNullableRole" => { allOf: [:$ref => "#/components/schemas/SchemasTest.Role"], nullable: true },
+                   "fieldNullableNotRequiredRole" => { allOf: [:$ref => "#/components/schemas/SchemasTest.Role"], nullable: true },
                    "fieldRoles" => { items: { :$ref => "#/components/schemas/SchemasTest.Role" }, type: :array },
                    "fieldIntegers" => { items: { type: :number }, type: :array },
                    "fieldNullableString" => { type: :string, nullable: true },