diff --git a/src/dotty/DottyPredef.scala b/src/dotty/DottyPredef.scala
index 0c2492c94725..5fa3b0bf4115 100644
--- a/src/dotty/DottyPredef.scala
+++ b/src/dotty/DottyPredef.scala
@@ -1,37 +1,20 @@
 package dotty
 
-import scala.reflect.ClassTag
 import scala.reflect.runtime.universe.TypeTag
-import scala.Predef.???
+import scala.reflect.ClassTag
+import scala.Predef.{???, implicitly}
 
-abstract class I1 {
-  implicit def classTag[T]: ClassTag[T] = ???
+/** unimplemented implicit for TypeTag */
+object DottyPredef {
   implicit def typeTag[T]: TypeTag[T] = ???
-  implicit val DoubleClassTag: ClassTag[Double]   = ClassTag.Double
-}
-abstract class I2 extends I1 {
-  implicit val FloatClassTag: ClassTag[Double]   = ClassTag.Double
-}
-abstract class I3 extends I2 {
-  implicit val LongClassTag: ClassTag[Long]       = ClassTag.Long
-}
-abstract class I4 extends I3 {
-  implicit val IntClassTag: ClassTag[Int]         = ClassTag.Int
-}
-abstract class I5 extends I4 {
-  implicit val ShortClassTag: ClassTag[Short]     = ClassTag.Short
-}
-abstract class I6 extends I5 {
-  implicit val ByteClassTag: ClassTag[Byte]       = ClassTag.Byte
-  implicit val CharClassTag: ClassTag[Char]       = ClassTag.Char
-  implicit val BooleanClassTag: ClassTag[Boolean] = ClassTag.Boolean
-  implicit val UnitClassTag: ClassTag[Unit]       = ClassTag.Unit
-  implicit val NullClassTag: ClassTag[Null]       = ClassTag.Null
-}
 
-/** implicits for ClassTag and TypeTag. Should be implemented with macros */
-object DottyPredef extends I6 {
+  implicit def arrayTag[T](implicit ctag: ClassTag[T]): ClassTag[Array[T]] = {
+    val ctag1 =
+      if (ctag == ClassTag.Unit) implicitly[ClassTag[scala.runtime.BoxedUnit]]
+      else ctag
+    ctag1.wrap.asInstanceOf[ClassTag[Array[T]]]
+  }
 
-  /** ClassTags for final classes */
-  implicit val NothingClassTag: ClassTag[Nothing] = ClassTag.Nothing
+  def classOf[T](implicit ctag: ClassTag[T]): Class[T] =
+    ctag.runtimeClass.asInstanceOf[Class[T]]
 }
diff --git a/src/dotty/tools/backend/jvm/DottyBackendInterface.scala b/src/dotty/tools/backend/jvm/DottyBackendInterface.scala
index 5776cc8e234f..2e57b499650a 100644
--- a/src/dotty/tools/backend/jvm/DottyBackendInterface.scala
+++ b/src/dotty/tools/backend/jvm/DottyBackendInterface.scala
@@ -179,14 +179,14 @@ class DottyBackendInterface(outputDirectory: AbstractFile)(implicit ctx: Context
   implicit val ApplyTag: ClassTag[Apply] = ClassTag[Apply](classOf[Apply])
   implicit val SelectTag: ClassTag[Select] = ClassTag[Select](classOf[Select])
   implicit val TypeApplyTag: ClassTag[TypeApply] = ClassTag[TypeApply](classOf[TypeApply])
-  implicit val ClassDefTag: ClassTag[ClassDef] = ClassTag[TypeDef](classOf[TypeDef])
+           val ClassDefTag: ClassTag[ClassDef] = ClassTag[TypeDef](classOf[TypeDef]) // no implicit, it's an alias of TypeDefTag
   implicit val TryTag: ClassTag[Try] = ClassTag[Try](classOf[Try])
   implicit val AssignTag: ClassTag[Assign] = ClassTag[Assign](classOf[Assign])
   implicit val IdentTag: ClassTag[Ident] = ClassTag[Ident](classOf[Ident])
   implicit val IfTag: ClassTag[If] = ClassTag[If](classOf[If])
-  implicit val LabelDefTag: ClassTag[LabelDef] = ClassTag[LabelDef](classOf[LabelDef])
+           val LabelDefTag: ClassTag[LabelDef] = ClassTag[LabelDef](classOf[LabelDef]) // no implicit, it's an alias of DefDefTag
   implicit val ValDefTag: ClassTag[ValDef] = ClassTag[ValDef](classOf[ValDef])
-  implicit val ThrowTag: ClassTag[Throw] = ClassTag[Throw](classOf[Throw])
+           val ThrowTag: ClassTag[Throw] = ClassTag[Throw](classOf[Throw]) // no implicit, it's an alias of ApplyTag
   implicit val ReturnTag: ClassTag[Return] = ClassTag[Return](classOf[Return])
   implicit val LiteralTag: ClassTag[Literal] = ClassTag[Literal](classOf[Literal])
   implicit val BlockTag: ClassTag[Block] = ClassTag[Block](classOf[Block])
@@ -197,12 +197,12 @@ class DottyBackendInterface(outputDirectory: AbstractFile)(implicit ctx: Context
   implicit val ThisTag: ClassTag[This] = ClassTag[This](classOf[This])
   implicit val AlternativeTag: ClassTag[Alternative] = ClassTag[Alternative](classOf[Alternative])
   implicit val DefDefTag: ClassTag[DefDef] = ClassTag[DefDef](classOf[DefDef])
-  implicit val ModuleDefTag: ClassTag[ModuleDef] = ClassTag[ModuleDef](classOf[ModuleDef])
+           val ModuleDefTag: ClassTag[ModuleDef] = ClassTag[ModuleDef](classOf[ModuleDef]) // no implicit, it's an alias of NullTag
   implicit val NameTag: ClassTag[Name] = ClassTag[Name](classOf[Name])
   implicit val TemplateTag: ClassTag[Template] = ClassTag[Template](classOf[Template])
   implicit val BindTag: ClassTag[Bind] = ClassTag[Bind](classOf[Bind])
   implicit val NewTag: ClassTag[New] = ClassTag[New](classOf[New])
-  implicit val ApplyDynamicTag: ClassTag[ApplyDynamic] = ClassTag[ApplyDynamic](classOf[ApplyDynamic])
+           val ApplyDynamicTag: ClassTag[ApplyDynamic] = ClassTag[ApplyDynamic](classOf[ApplyDynamic]) // no implicit, it's an alias of NullTag
   implicit val SuperTag: ClassTag[Super] = ClassTag[Super](classOf[Super])
   implicit val ConstantClassTag: ClassTag[Constant] = ClassTag[Constant](classOf[Constant])
   implicit val ClosureTag: ClassTag[Closure] = ClassTag[Closure](classOf[Closure])
diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index 99b7bd880fff..7c7648657d03 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -59,7 +59,6 @@ class Compiler {
            new SeqLiterals,
            new InterceptedMethods,
            new Getters,
-           new ClassTags,
            new ElimByName,
            new AugmentScala2Traits,
            new ResolveSuper),
diff --git a/src/dotty/tools/dotc/ast/Desugar.scala b/src/dotty/tools/dotc/ast/Desugar.scala
index 87694843ad6a..b59121462f82 100644
--- a/src/dotty/tools/dotc/ast/Desugar.scala
+++ b/src/dotty/tools/dotc/ast/Desugar.scala
@@ -147,18 +147,7 @@ object desugar {
         tparam
     }
 
-    val meth1 = epbuf.toList match {
-      case Nil =>
-        meth
-      case evidenceParams =>
-        val vparamss1 = vparamss.reverse match {
-          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
-            ((vparams ++ evidenceParams) :: rvparamss).reverse
-          case _ =>
-            vparamss :+ evidenceParams
-        }
-        cpy.DefDef(meth)(tparams = tparams1, vparamss = vparamss1)
-    }
+    val meth1 = addEvidenceParams(cpy.DefDef(meth)(tparams = tparams1), epbuf.toList)
 
     /** The longest prefix of parameter lists in vparamss whose total length does not exceed `n` */
     def takeUpTo(vparamss: List[List[ValDef]], n: Int): List[List[ValDef]] = vparamss match {
@@ -204,6 +193,30 @@ object desugar {
     }
   }
 
+  // Add all evidence parameters in `params` as implicit parameters to `meth` */
+  private def addEvidenceParams(meth: DefDef, params: List[ValDef])(implicit ctx: Context): DefDef =
+    params match {
+      case Nil =>
+        meth
+      case evidenceParams =>
+        val vparamss1 = meth.vparamss.reverse match {
+          case (vparams @ (vparam :: _)) :: rvparamss if vparam.mods is Implicit =>
+            ((vparams ++ evidenceParams) :: rvparamss).reverse
+          case _ =>
+            meth.vparamss :+ evidenceParams
+        }
+        cpy.DefDef(meth)(vparamss = vparamss1)
+    }
+
+  /** The implicit evidence parameters of `meth`, as generated by `desugar.defDef` */
+  private def evidenceParams(meth: DefDef)(implicit ctx: Context): List[ValDef] =
+    meth.vparamss.reverse match {
+      case (vparams @ (vparam :: _)) :: _ if vparam.mods is Implicit =>
+        vparams.dropWhile(!_.name.startsWith(nme.EVIDENCE_PARAM_PREFIX))
+      case _ =>
+        Nil
+    }
+
   /** Fill in empty type bounds with Nothing/Any. Expand private local type parameters as follows:
    *
    *     class C[v T]
@@ -255,10 +268,13 @@ object desugar {
       else constr1.vparamss.nestedMap(toDefParam)
     val constr = cpy.DefDef(constr1)(tparams = constrTparams, vparamss = constrVparamss)
 
-    // Add constructor type parameters to auxiliary constructors
+    // Add constructor type parameters and evidence implicit parameters
+    // to auxiliary constructors
     val normalizedBody = impl.body map {
       case ddef: DefDef if ddef.name.isConstructorName =>
-        cpy.DefDef(ddef)(tparams = constrTparams)
+        addEvidenceParams(
+          cpy.DefDef(ddef)(tparams = constrTparams),
+          evidenceParams(constr1).map(toDefParam))
       case stat =>
         stat
     }
diff --git a/src/dotty/tools/dotc/ast/tpd.scala b/src/dotty/tools/dotc/ast/tpd.scala
index b78e4c79f3b2..a0400c1e84f8 100644
--- a/src/dotty/tools/dotc/ast/tpd.scala
+++ b/src/dotty/tools/dotc/ast/tpd.scala
@@ -777,27 +777,6 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       }
       else Assign(tree, rhs)
 
-    /** A tree in place of this tree that represents the class of type `tp`.
-     *  Contains special handling if the class is a primitive value class
-     *  and invokes a `default` method otherwise.
-     */
-    def clsOf(tp: Type, default: => Tree)(implicit ctx: Context): Tree = {
-      def TYPE(module: TermSymbol) =
-        ref(module).select(nme.TYPE_).ensureConforms(tree.tpe).withPos(tree.pos)
-      defn.scalaClassName(tp) match {
-        case tpnme.Boolean => TYPE(defn.BoxedBooleanModule)
-        case tpnme.Byte => TYPE(defn.BoxedByteModule)
-        case tpnme.Short => TYPE(defn.BoxedShortModule)
-        case tpnme.Char => TYPE(defn.BoxedCharModule)
-        case tpnme.Int => TYPE(defn.BoxedIntModule)
-        case tpnme.Long => TYPE(defn.BoxedLongModule)
-        case tpnme.Float => TYPE(defn.BoxedFloatModule)
-        case tpnme.Double => TYPE(defn.BoxedDoubleModule)
-        case tpnme.Unit => TYPE(defn.BoxedUnitModule)
-        case _ => default
-      }
-    }
-
     // --- Higher order traversal methods -------------------------------
 
     /** Apply `f` to each subtree of this tree */
@@ -842,6 +821,23 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
     }
   }
 
+  /** A tree that represents the class of the erasure of type `tp`. */
+  def clsOf(tp: Type)(implicit ctx: Context): Tree = {
+    def TYPE(module: TermSymbol) = ref(module).select(nme.TYPE_)
+    defn.scalaClassName(tp) match {
+      case tpnme.Boolean => TYPE(defn.BoxedBooleanModule)
+      case tpnme.Byte => TYPE(defn.BoxedByteModule)
+      case tpnme.Short => TYPE(defn.BoxedShortModule)
+      case tpnme.Char => TYPE(defn.BoxedCharModule)
+      case tpnme.Int => TYPE(defn.BoxedIntModule)
+      case tpnme.Long => TYPE(defn.BoxedLongModule)
+      case tpnme.Float => TYPE(defn.BoxedFloatModule)
+      case tpnme.Double => TYPE(defn.BoxedDoubleModule)
+      case tpnme.Unit => TYPE(defn.BoxedUnitModule)
+      case _ => Literal(Constant(TypeErasure.erasure(tp)))
+    }
+  }
+
   def applyOverloaded(receiver: Tree, method: TermName, args: List[Tree], targs: List[Type], expectedType: Type, isAnnotConstructor: Boolean = false)(implicit ctx: Context): Tree = {
     val typer = ctx.typer
     val proto = new FunProtoTyped(args, expectedType, typer)
diff --git a/src/dotty/tools/dotc/core/Definitions.scala b/src/dotty/tools/dotc/core/Definitions.scala
index c5d42a4728e9..188a00fc2683 100644
--- a/src/dotty/tools/dotc/core/Definitions.scala
+++ b/src/dotty/tools/dotc/core/Definitions.scala
@@ -419,6 +419,9 @@ class Definitions {
   lazy val LanguageModuleRef          = ctx.requiredModule("dotty.language")
   def LanguageModuleClass(implicit ctx: Context) = LanguageModuleRef.symbol.moduleClass.asClass
   lazy val NonLocalReturnControlType: TypeRef   = ctx.requiredClassRef("scala.runtime.NonLocalReturnControl")
+  lazy val ClassTagType = ctx.requiredClassRef("scala.reflect.ClassTag")
+  def ClassTagClass(implicit ctx: Context) = ClassTagType.symbol.asClass
+  def ClassTagModule(implicit ctx: Context) = ClassTagClass.companionModule
 
   // Annotation base classes
   lazy val AnnotationType              = ctx.requiredClassRef("scala.annotation.Annotation")
diff --git a/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 81d19f7e48eb..16caac02e20b 100644
--- a/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -290,6 +290,8 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
           ConstantType(Constant(readName().toString))
         case NULLconst =>
           ConstantType(Constant(null))
+        case CLASSconst =>
+          ConstantType(Constant(readType()))
         case BYNAMEtype =>
           ExprType(readType())
       }
diff --git a/src/dotty/tools/dotc/transform/ClassOf.scala b/src/dotty/tools/dotc/transform/ClassOf.scala
index 51a68f9033e5..93aca1b74ca9 100644
--- a/src/dotty/tools/dotc/transform/ClassOf.scala
+++ b/src/dotty/tools/dotc/transform/ClassOf.scala
@@ -15,6 +15,11 @@ import TreeTransforms.{MiniPhaseTransform, TransformerInfo, TreeTransform}
  *    classOf[C]    -> B.TYPE
  *  For every non-primitive class D:
  *    classOf[D]    -> Literal(Constant(erasure(D)))
+ *
+ *  NOTE: This is almost redundant since classOf now resolves
+ *  to DottyPredef.classOf, which does not need the transform. The phase
+ *  is kept in in order not to crash if someone calls Predef.classOf.
+ *  Once we have merged Predef and DottyPredef, the phase can be dropped.
  */
 class ClassOf extends MiniPhaseTransform {
   import tpd._
@@ -31,7 +36,7 @@ class ClassOf extends MiniPhaseTransform {
   override def transformTypeApply(tree: TypeApply)(implicit ctx: Context, info: TransformerInfo): Tree =
     if (tree.symbol eq classOfMethod) {
       val targ = tree.args.head.tpe
-      tree.clsOf(targ, Literal(Constant(TypeErasure.erasure(targ))))
+      clsOf(targ).ensureConforms(tree.tpe).withPos(tree.pos)
     }
     else tree
 }
diff --git a/src/dotty/tools/dotc/transform/GetClass.scala b/src/dotty/tools/dotc/transform/GetClass.scala
index 9d182382d211..f25fd6f64128 100644
--- a/src/dotty/tools/dotc/transform/GetClass.scala
+++ b/src/dotty/tools/dotc/transform/GetClass.scala
@@ -5,6 +5,7 @@ import ast.tpd
 import core.Contexts.Context
 import core.StdNames.nme
 import core.Phases.Phase
+import TypeUtils._
 import TreeTransforms.{MiniPhaseTransform, TransformerInfo}
 
 /** Rewrite `getClass` calls as follow:
@@ -24,7 +25,8 @@ class GetClass extends MiniPhaseTransform {
   override def transformApply(tree: Apply)(implicit ctx: Context, info: TransformerInfo): Tree = {
     import ast.Trees._
     tree match {
-      case Apply(Select(qual, nme.getClass_), Nil) => tree.clsOf(qual.tpe.widen, tree)
+      case Apply(Select(qual, nme.getClass_), Nil) if qual.tpe.widen.isPrimitiveValueType =>
+        clsOf(qual.tpe.widen).withPos(tree.pos)
       case _ => tree
     }
   }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 854bc2094dea..4d0efe875da8 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1454,7 +1454,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
               case ambi: AmbiguousImplicits =>
                 implicitArgError(s"ambiguous implicits: ${ambi.explanation} of $where")
               case failure: SearchFailure =>
-                implicitArgError(d"no implicit argument of type $formal found for $where" + failure.postscript)
+                val arg = synthesizedClassTag(formal)
+                if (!arg.isEmpty) arg
+                else implicitArgError(d"no implicit argument of type $formal found for $where" + failure.postscript)
             }
           }
           if (errors.nonEmpty) {
@@ -1515,6 +1517,28 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
         }
     }
 
+    /** If `formal` is of the form ClassTag[T], where `T` is a class type,
+     *  synthesize a class tag for `T`.
+     */
+    def synthesizedClassTag(formal: Type): Tree = {
+      if (formal.isRef(defn.ClassTagClass))
+        formal.argTypes match {
+          case arg :: Nil =>
+            val tp = fullyDefinedType(arg, "ClassTag argument", tree.pos)
+            tp.underlyingClassRef(refinementOK = false) match {
+              case tref: TypeRef =>
+                return ref(defn.ClassTagModule)
+                  .select(nme.apply)
+                  .appliedToType(tp)
+                  .appliedTo(clsOf(tref))
+                  .withPos(tree.pos.endPos)
+              case _ =>
+            }
+          case _ =>
+        }
+      EmptyTree
+    }
+
     /** Adapt an expression of constant type to a different constant type `tpe`. */
     def adaptConstant(tree: Tree, tpe: ConstantType): Tree = {
       def lit = Literal(tpe.value).withPos(tree.pos)
diff --git a/test/dotc/tests.scala b/test/dotc/tests.scala
index 70af32bd3d53..9d9c0e8e9b1a 100644
--- a/test/dotc/tests.scala
+++ b/test/dotc/tests.scala
@@ -144,6 +144,7 @@ class tests extends CompilerTest {
   @Test def neg_variancesConstr = compileFile(negDir, "variances-constr", xerrors = 2)
   @Test def neg_i871_missingReturnType = compileFile(negDir, "i871", xerrors = 2)
   @Test def neg_badAuxConstr = compileFile(negDir, "badAuxConstr", xerrors = 2)
+  @Test def neg_classOf = compileFile(negDir, "classOf", xerrors = 4)
   @Test def neg_typetest = compileFile(negDir, "typetest", xerrors = 1)
   @Test def neg_t1569_failedAvoid = compileFile(negDir, "t1569-failedAvoid", xerrors = 1)
   @Test def neg_clashes = compileFile(negDir, "clashes", xerrors = 2)
@@ -174,7 +175,6 @@ class tests extends CompilerTest {
   @Test def neg_selfInheritance = compileFile(negDir, "selfInheritance", xerrors = 6)
   @Test def neg_selfreq = compileFile(negDir, "selfreq", xerrors = 2)
   @Test def neg_singletons = compileFile(negDir, "singletons", xerrors = 8)
-  @Test def neg_shadowedImplicits = compileFile(negDir, "arrayclone-new", xerrors = 2)
   @Test def neg_ski = compileFile(negDir, "ski", xerrors = 12)
   @Test def neg_traitParamsTyper = compileFile(negDir, "traitParamsTyper", xerrors = 5)
   @Test def neg_traitParamsMixin = compileFile(negDir, "traitParamsMixin", xerrors = 2)
diff --git a/tests/neg/arrayclone-new.scala b/tests/neg/arrayclone-new.scala
deleted file mode 100644
index 4e33a7d8cde6..000000000000
--- a/tests/neg/arrayclone-new.scala
+++ /dev/null
@@ -1,38 +0,0 @@
-// Run with -explaintypes to see information about shadowing failures
-import scala.reflect.{ClassTag, classTag}
-
-object Test extends dotty.runtime.LegacyApp{
-  ObjectArrayClone;
-  PolymorphicArrayClone;
-}
-
-object ObjectArrayClone{
-  val it : Array[String] = Array("1", "0");
-  val cloned = it.clone();
-  assert(cloned.sameElements(it));
-  cloned(0) = "0";
-  assert(it(0) == "1")
-}
-
-object PolymorphicArrayClone{
-  def testIt[T](it : Array[T], one : T, zero : T) = {
-    val cloned = it.clone();
-    assert(cloned.sameElements(it));
-    cloned(0) = zero;
-    assert(it(0) == one)
-  }
-
-  testIt(Array("one", "two"), "one", "two");
-
-  class Mangler[T: ClassTag](ts : T*){
-    // this will always be a BoxedAnyArray even after we've unboxed its contents.
-    val it = ts.toArray[T];
-  }
-
-  val mangled = new Mangler[Int](0, 1);
-
-  val y : Array[Int] = mangled.it; // make sure it's unboxed
-
-  testIt(mangled.it, 0, 1);
-}
-
diff --git a/tests/neg/classOf.scala b/tests/neg/classOf.scala
new file mode 100644
index 000000000000..e13cf71c43a2
--- /dev/null
+++ b/tests/neg/classOf.scala
@@ -0,0 +1,11 @@
+object Test {
+
+  class C { type I }
+  type A = C
+
+  def f1[T] = classOf[T] // error
+  def f2[T <: String] = classOf[T] // error
+  val x = classOf[Test.type] // error
+  val y = classOf[C { type I = String }] // error
+  val z = classOf[A] // ok
+}