diff --git a/compiler/src/dotty/tools/dotc/ast/Desugar.scala b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
index 493a515d1acc..8f4643d3b7fe 100644
--- a/compiler/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/compiler/src/dotty/tools/dotc/ast/Desugar.scala
@@ -338,8 +338,9 @@ object desugar {
       case _ => false
     }
 
-    val isCaseClass  = mods.is(Case) && !mods.is(Module)
-    val isCaseObject = mods.is(Case) && mods.is(Module)
+    val isObject = mods.is(Module)
+    val isCaseClass  = mods.is(Case) && !isObject
+    val isCaseObject = mods.is(Case) && isObject
     val isImplicit = mods.is(Implicit)
     val isEnum = mods.isEnumClass && !mods.is(Module)
     def isEnumCase = mods.isEnumCase
@@ -522,6 +523,8 @@ object desugar {
       parents1 = enumClassTypeRef :: Nil
     if (isCaseClass | isCaseObject)
       parents1 = parents1 :+ scalaDot(str.Product.toTypeName) :+ scalaDot(nme.Serializable.toTypeName)
+    else if (isObject)
+      parents1 = parents1 :+ scalaDot(nme.Serializable.toTypeName)
     if (isEnum)
       parents1 = parents1 :+ ref(defn.EnumType)