diff --git a/compiler/src/dotty/tools/dotc/transform/Mixin.scala b/compiler/src/dotty/tools/dotc/transform/Mixin.scala
index fe107c7c5556..4be96b2919cc 100644
--- a/compiler/src/dotty/tools/dotc/transform/Mixin.scala
+++ b/compiler/src/dotty/tools/dotc/transform/Mixin.scala
@@ -123,7 +123,7 @@ class Mixin extends MiniPhase with SymTransformer { thisPhase =>
         else sym.copySymDenotation(initFlags = sym.flags &~ ParamAccessor | Deferred)
       sym1.ensureNotPrivate
     }
-    else if (sym.isConstructor && sym.owner.is(Trait, butNot = Scala2x))
+    else if (sym.isConstructor && (sym.owner.is(Trait, butNot = Scala2x) || (sym.owner.isAllOf(Trait | Scala2x) && ctx.settings.scalajs.value)))
       sym.copySymDenotation(
         name = nme.TRAIT_CONSTRUCTOR,
         info = MethodType(Nil, sym.info.resultType))
diff --git a/project/Build.scala b/project/Build.scala
index daea2b962781..50c672ab72af 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -999,22 +999,22 @@ object Build {
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/net" ** "*.scala").get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/security" ** "*.scala").get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/util/regex" ** "*.scala").get
-          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/util/concurrent" ** (("*.scala": FileFilter) -- "ConcurrentHashMapTest.scala" -- "ConcurrentLinkedQueueTest.scala" -- "ConcurrentMapTest.scala" -- "ConcurrentSkipListSetTest.scala" -- "CopyOnWriteArrayListTest.scala")).get
+          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/util/concurrent" ** "*.scala").get
 
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/javalib/util" * (("*.scala": FileFilter)
-            -- "AbstractCollectionTest.scala" -- "AbstractListTest.scala" -- "AbstractMapTest.scala" -- "AbstractSetTest.scala" -- "ArrayDequeTest.scala" -- "ArrayListTest.scala"
-            -- "CollectionTest.scala" -- "CollectionsOnCheckedCollectionTest.scala" -- "CollectionsOnCheckedListTest.scala" -- "CollectionsOnCheckedMapTest.scala" -- "CollectionsOnCheckedSetTest.scala"
+            -- "AbstractListTest.scala" -- "AbstractMapTest.scala" -- "AbstractSetTest.scala" -- "ArrayDequeTest.scala" -- "ArrayListTest.scala"
+            -- "CollectionsOnCheckedCollectionTest.scala" -- "CollectionsOnCheckedListTest.scala" -- "CollectionsOnCheckedMapTest.scala" -- "CollectionsOnCheckedSetTest.scala"
             -- "CollectionsOnCollectionsTest.scala" -- "CollectionsOnListsTest.scala" -- "CollectionsOnMapsTest.scala" -- "CollectionsOnSetFromMapTest.scala" -- "CollectionsOnSetsTest.scala"
             -- "CollectionsOnSynchronizedCollectionTest.scala" -- "CollectionsOnSynchronizedListTest.scala" -- "CollectionsOnSynchronizedMapTest.scala" -- "CollectionsOnSynchronizedSetTest.scala" -- "CollectionsTest.scala"
             -- "DequeTest.scala" -- "EventObjectTest.scala" -- "FormatterTest.scala" -- "HashMapTest.scala" -- "HashSetTest.scala" -- "IdentityHashMapTest.scala"
-            -- "LinkedHashMapTest.scala" -- "LinkedHashSetTest.scala" -- "LinkedListTest.scala" -- "ListTest.scala" -- "MapTest.scala"
-            -- "NavigableSetTest.scala" -- "PriorityQueueTest.scala" -- "SetTest.scala" -- "SortedMapTest.scala" -- "SortedSetTest.scala" -- "TreeSetTest.scala")).get
+            -- "LinkedHashMapTest.scala" -- "LinkedHashSetTest.scala" -- "LinkedListTest.scala"
+            -- "PriorityQueueTest.scala"  -- "SortedMapTest.scala" -- "SortedSetTest.scala" -- "TreeSetTest.scala")).get
 
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/utils" ** "*.scala").get
-          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/junit" ** (("*.scala": FileFilter))).get
+          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/junit" ** "*.scala").get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/niobuffer" ** (("*.scala": FileFilter)  -- "ByteBufferTest.scala")).get
           ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/niocharset" ** (("*.scala": FileFilter)  -- "BaseCharsetTest.scala" -- "Latin1Test.scala" -- "USASCIITest.scala" -- "UTF16Test.scala" -- "UTF8Test.scala")).get
-          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/scalalib" ** (("*.scala": FileFilter)  -- "ArrayBuilderTest.scala" -- "ClassTagTest.scala" -- "EnumerationTest.scala" -- "RangesTest.scala" -- "SymbolTest.scala")).get
+          ++ (dir / "shared/src/test/scala/org/scalajs/testsuite/scalalib" ** (("*.scala": FileFilter)  -- "ArrayBuilderTest.scala" -- "ClassTagTest.scala" -- "EnumerationTest.scala" -- "SymbolTest.scala")).get
           ++ (dir / "shared/src/test/require-sam" ** "*.scala").get
           ++ (dir / "shared/src/test/require-jdk8/org/scalajs/testsuite/compiler" ** (("*.scala": FileFilter) -- "DefaultMethodsTest.scala")).get
           ++ (dir / "shared/src/test/require-jdk8/org/scalajs/testsuite/javalib/lang" ** "*.scala").get