diff --git a/src/ameba/severity.cr b/src/ameba/severity.cr
index 19e5a809..52dd7455 100644
--- a/src/ameba/severity.cr
+++ b/src/ameba/severity.cr
@@ -54,7 +54,7 @@ module Ameba
 
       case value = node.value
       when String then Severity.parse(value)
-      when Nil    then nil
+      when Nil    then raise "Missing severity"
       else
         raise "Incorrect severity: #{value}"
       end