diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala b/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
index 44305412e09c..f082765d6cb7 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
@@ -198,6 +198,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   SCALA2X                             // Imported from Scala2.x
                   DEFAULTparameterized                // Method with default parameters
                   STABLE                              // Method that is assumed to be stable
+                  PARAMsetter                         // A setter without a body named `x_=` where `x` is pickled as a PARAM
                   Annotation
 
   Annotation    = ANNOTATION     Length tycon_Type fullAnnotation_Term
@@ -226,8 +227,8 @@ Standard Section: "Positions" Assoc*
 object TastyFormat {
 
   final val header = Array(0x5C, 0xA1, 0xAB, 0x1F)
-  val MajorVersion = 5
-  val MinorVersion = 1
+  val MajorVersion = 6
+  val MinorVersion = 0
 
   /** Tags used to serialize names */
   class NameTags {
@@ -268,6 +269,7 @@ object TastyFormat {
   // AST tags
   // Cat. 1:    tag
 
+  final val firstSimpleTreeTag = UNITconst
   final val UNITconst = 2
   final val FALSEconst = 3
   final val TRUEconst = 4
@@ -300,6 +302,7 @@ object TastyFormat {
   final val STABLE = 31
   final val MACRO = 32
   final val ERASED = 33
+  final val PARAMsetter = 34
 
   // Cat. 2:    tag Nat
 
@@ -417,7 +420,6 @@ object TastyFormat {
 
   final val HOLE = 255
 
-  final val firstSimpleTreeTag = UNITconst
   final val firstNatTreeTag = SHAREDterm
   final val firstASTTreeTag = THIS
   final val firstNatASTTreeTag = IDENT
@@ -425,7 +427,7 @@ object TastyFormat {
 
   /** Useful for debugging */
   def isLegalTag(tag: Int) =
-    firstSimpleTreeTag <= tag && tag <= ERASED ||
+    firstSimpleTreeTag <= tag && tag <= PARAMsetter ||
     firstNatTreeTag <= tag && tag <= SYMBOLconst ||
     firstASTTreeTag <= tag && tag <= SINGLETONtpt ||
     firstNatASTTreeTag <= tag && tag <= NAMEDARG ||
@@ -463,6 +465,7 @@ object TastyFormat {
        | SCALA2X
        | DEFAULTparameterized
        | STABLE
+       | PARAMsetter
        | ANNOTATION
        | PRIVATEqualified
        | PROTECTEDqualified => true
@@ -518,6 +521,7 @@ object TastyFormat {
     case SCALA2X => "SCALA2X"
     case DEFAULTparameterized => "DEFAULTparameterized"
     case STABLE => "STABLE"
+    case PARAMsetter => "PARAMsetter"
 
     case SHAREDterm => "SHAREDterm"
     case SHAREDtype => "SHAREDtype"
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
index 7fd249d9f260..f7d942b4bdad 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
@@ -601,6 +601,7 @@ class TreePickler(pickler: TastyPickler) {
       if (flags is CaseAccessor) writeByte(CASEaccessor)
       if (flags is DefaultParameterized) writeByte(DEFAULTparameterized)
       if (flags is Stable) writeByte(STABLE)
+      if ((flags is ParamAccessor) && sym.isSetter) writeByte(PARAMsetter)
     } else {
       if (flags is Sealed) writeByte(SEALED)
       if (flags is Abstract) writeByte(ABSTRACT)
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index e33da8eabba1..ddf3ef7ed765 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -424,7 +424,11 @@ class TreeUnpickler(reader: TastyReader,
         flags = flags | (if (tag == VALDEF) ModuleValCreationFlags else ModuleClassCreationFlags)
       if (ctx.owner.isClass) {
         if (tag == TYPEPARAM) flags |= Param
-        else if (tag == PARAM) flags |= ParamAccessor
+        else if (tag == PARAM) {
+          flags |= ParamAccessor
+          if (!rhsIsEmpty) // param alias
+            flags |= Method
+        }
       }
       else if (isParamTag(tag)) flags |= Param
       flags
@@ -585,6 +589,8 @@ class TreeUnpickler(reader: TastyReader,
           case SCALA2X => addFlag(Scala2x)
           case DEFAULTparameterized => addFlag(DefaultParameterized)
           case STABLE => addFlag(Stable)
+          case PARAMsetter =>
+            addFlag(ParamAccessor)
           case PRIVATEqualified =>
             readByte()
             privateWithin = readType().typeSymbol
@@ -728,11 +734,6 @@ class TreeUnpickler(reader: TastyReader,
               vparamss.nestedMap(_.symbol), name == nme.CONSTRUCTOR)
           val resType = ctx.effectiveResultType(sym, typeParams, tpt.tpe)
           sym.info = ctx.methodType(typeParams, valueParamss, resType)
-          if (sym.isSetter && sym.accessedFieldOrGetter.is(ParamAccessor)) {
-            // reconstitute ParamAccessor flag of setters for var parameters, which is not pickled
-            sym.setFlag(ParamAccessor)
-            sym.resetFlag(Deferred)
-          }
           DefDef(tparams, vparamss, tpt)
         case VALDEF =>
           val tpt = readTpt()(localCtx)
@@ -775,7 +776,6 @@ class TreeUnpickler(reader: TastyReader,
             ValDef(tpt)
           }
           else {
-            sym.setFlag(Method)
             sym.info = ExprType(tpt.tpe)
             pickling.println(i"reading param alias $name -> $currentAddr")
             DefDef(Nil, Nil, tpt)