diff --git a/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala b/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
index 7dbb62e43680..3245e5b12e5e 100644
--- a/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
+++ b/compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala
@@ -91,7 +91,7 @@ class TreeTypeMap(
         case id: Ident if tpd.needsSelect(id.tpe) =>
           ref(id.tpe.asInstanceOf[TermRef]).withSpan(id.span)
         case ddef @ DefDef(name, tparams, vparamss, tpt, _) =>
-          val (tmap1, tparams1) = transformDefs(ddef.tparams)
+          val (tmap1, tparams1) = transformDefs(tparams)
           val (tmap2, vparamss1) = tmap1.transformVParamss(vparamss)
           val res = cpy.DefDef(ddef)(name, tparams1, vparamss1, tmap2.transform(tpt), tmap2.transform(ddef.rhs))
           res.symbol.setParamssFromDefs(tparams1, vparamss1)
diff --git a/compiler/src/dotty/tools/dotc/transform/HoistSuperArgs.scala b/compiler/src/dotty/tools/dotc/transform/HoistSuperArgs.scala
index 3d13ab89211b..7fd6c15375fe 100644
--- a/compiler/src/dotty/tools/dotc/transform/HoistSuperArgs.scala
+++ b/compiler/src/dotty/tools/dotc/transform/HoistSuperArgs.scala
@@ -33,7 +33,7 @@ object HoistSuperArgs {
  *
  *  An argument is complex if it contains a method or template definition, a this or a new,
  *  or it contains an identifier which needs a `this` prefix to be accessed. This is the case
- *  if the identifer neither a global reference nor a reference to a parameter of the enclosing class.
+ *  if the identifier has neither a global reference nor a reference to a parameter of the enclosing class.
  *  @see needsHoist for an implementation.
  *
  *  A hoisted argument definition gets the parameters of the class it is hoisted from
@@ -116,11 +116,18 @@ class HoistSuperArgs extends MiniPhase with IdentityDenotTransformer { thisPhase
         case _                    => false
       }
 
+      /** Only rewire types that are owned by the current Hoister and is an param or accessor */
+      def needsRewire(tp: Type) = tp match {
+        case ntp: NamedType =>
+          (ntp.symbol.owner == cls || ntp.symbol.owner == constr) && ntp.symbol.isParamOrAccessor
+        case _ => false
+      }
+
       // begin hoistSuperArg
       arg match {
         case Apply(fn, arg1 :: Nil) if fn.symbol == defn.cbnArg =>
           cpy.Apply(arg)(fn, hoistSuperArg(arg1, cdef) :: Nil)
-        case _ if (arg.existsSubTree(needsHoist)) =>
+        case _ if arg.existsSubTree(needsHoist) =>
           val superMeth = newSuperArgMethod(arg.tpe)
           val superArgDef = polyDefDef(superMeth, trefs => vrefss => {
             val paramSyms = trefs.map(_.typeSymbol) ::: vrefss.flatten.map(_.symbol)
@@ -128,9 +135,7 @@ class HoistSuperArgs extends MiniPhase with IdentityDenotTransformer { thisPhase
               typeMap = new TypeMap {
                 lazy val origToParam = origParams.zip(paramSyms).toMap
                 def apply(tp: Type) = tp match {
-                  case tp: NamedType
-                  if (tp.symbol.owner == cls || tp.symbol.owner == constr) &&
-                     tp.symbol.isParamOrAccessor =>
+                  case tp: NamedType if needsRewire(tp) =>
                     origToParam.get(tp.symbol) match {
                       case Some(mappedSym) => if (tp.symbol.isType) mappedSym.typeRef else mappedSym.termRef
                       case None => mapOver(tp)
@@ -140,7 +145,7 @@ class HoistSuperArgs extends MiniPhase with IdentityDenotTransformer { thisPhase
                 }
               },
               treeMap = {
-                case tree: RefTree if paramSyms.contains(tree.symbol) =>
+                case tree: RefTree if needsRewire(tree.tpe) =>
                   cpy.Ident(tree)(tree.name).withType(tree.tpe)
                 case tree =>
                   tree
diff --git a/compiler/src/dotty/tools/dotc/transform/ProtectedAccessors.scala b/compiler/src/dotty/tools/dotc/transform/ProtectedAccessors.scala
index 9e7d128901ac..85873b74670f 100644
--- a/compiler/src/dotty/tools/dotc/transform/ProtectedAccessors.scala
+++ b/compiler/src/dotty/tools/dotc/transform/ProtectedAccessors.scala
@@ -10,7 +10,7 @@ import MegaPhase.MiniPhase
 import config.Printers.transforms
 
 /** Add accessors for all protected accesses. An accessor is needed if
- *  according to the rules of the JVM a protected class member is not accesissible
+ *  according to the rules of the JVM a protected class member is not accessible
  *  from the point of access, but is accessible if the access is from an enclosing
  *  class. In this point a public access method is placed in that enclosing class.
  */
diff --git a/tests/pos/i8748.scala b/tests/pos/i8748.scala
new file mode 100644
index 000000000000..2aee8308394f
--- /dev/null
+++ b/tests/pos/i8748.scala
@@ -0,0 +1,9 @@
+class A(a: String) extends B(new C {
+  override def get(): String = a
+})
+
+class B(c: C)
+
+trait C {
+  def get(): String
+}
diff --git a/tests/pos/i8786.scala b/tests/pos/i8786.scala
new file mode 100644
index 000000000000..df58c3e9a553
--- /dev/null
+++ b/tests/pos/i8786.scala
@@ -0,0 +1,7 @@
+class B(y: Int) extends A(new C(y){})
+
+class A(c: C)
+
+abstract class C(y: Int) {
+  def x: Int = y
+}