diff --git a/spec/ameba/severity_spec.cr b/spec/ameba/severity_spec.cr
index 9fd17a21..3a19881f 100644
--- a/spec/ameba/severity_spec.cr
+++ b/spec/ameba/severity_spec.cr
@@ -45,7 +45,7 @@ module Ameba
     include YAML::Serializable
 
     @[YAML::Field(converter: Ameba::SeverityYamlConverter)]
-    property severity : Severity
+    property severity : Severity?
   end
 
   describe SeverityYamlConverter do