diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
index 79110b44dd5c..95dbaeb10267 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala
@@ -657,6 +657,7 @@ class TreePickler(pickler: TastyPickler) {
       assert(isModifierTag(tag))
       writeByte(tag)
     }
+    assert(!flags.is(Scala2x))
     if (flags.is(Private)) writeModTag(PRIVATE)
     if (flags.is(Protected)) writeModTag(PROTECTED)
     if (flags.is(Final, butNot = Module)) writeModTag(FINAL)
@@ -671,7 +672,6 @@ class TreePickler(pickler: TastyPickler) {
     if (flags.is(Local)) writeModTag(LOCAL)
     if (flags.is(Synthetic)) writeModTag(SYNTHETIC)
     if (flags.is(Artifact)) writeModTag(ARTIFACT)
-    if (flags.is(Scala2x)) writeModTag(SCALA2X)
     if (isTerm) {
       if (flags.is(Implicit)) writeModTag(IMPLICIT)
       if (flags.is(Given)) writeModTag(GIVEN)
diff --git a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 48b7450bcd72..4978b7847f8c 100644
--- a/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -647,7 +647,6 @@ class TreeUnpickler(reader: TastyReader,
           case CASEaccessor => addFlag(CaseAccessor)
           case COVARIANT => addFlag(Covariant)
           case CONTRAVARIANT => addFlag(Contravariant)
-          case SCALA2X => addFlag(Scala2x)
           case HASDEFAULT => addFlag(HasDefault)
           case STABLE => addFlag(StableRealizable)
           case EXTENSION => addFlag(Extension)
diff --git a/tasty/src/dotty/tools/tasty/TastyFormat.scala b/tasty/src/dotty/tools/tasty/TastyFormat.scala
index 7ac7f05c9d6a..f330254e4ff2 100644
--- a/tasty/src/dotty/tools/tasty/TastyFormat.scala
+++ b/tasty/src/dotty/tools/tasty/TastyFormat.scala
@@ -197,7 +197,6 @@ Standard-Section: "ASTs" TopLevelStat*
                   CASEaccessor                                                     -- A getter for a case class parameter
                   COVARIANT                                                        -- A type parameter marked “+”
                   CONTRAVARIANT                                                    -- A type parameter marked “-”
-                  SCALA2X                                                          -- Imported from Scala2.x
                   HASDEFAULT                                                       -- Parameter with default arg; method with default parameters (default arguments are separate methods with DEFAULTGETTER names)
                   STABLE                                                           -- Method that is assumed to be stable, i.e. its applications are legal paths
                   EXTENSION                                                        -- An extension method
@@ -343,7 +342,6 @@ object TastyFormat {
   final val CASEaccessor = 27
   final val COVARIANT = 28
   final val CONTRAVARIANT = 29
-  final val SCALA2X = 30
   final val HASDEFAULT = 31
   final val STABLE = 32
   final val MACRO = 33
@@ -507,7 +505,6 @@ object TastyFormat {
        | CASEaccessor
        | COVARIANT
        | CONTRAVARIANT
-       | SCALA2X
        | HASDEFAULT
        | STABLE
        | EXTENSION
@@ -568,7 +565,6 @@ object TastyFormat {
     case CASEaccessor => "CASEaccessor"
     case COVARIANT => "COVARIANT"
     case CONTRAVARIANT => "CONTRAVARIANT"
-    case SCALA2X => "SCALA2X"
     case HASDEFAULT => "HASDEFAULT"
     case STABLE => "STABLE"
     case EXTENSION => "EXTENSION"