diff --git a/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala b/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
index 3fafcef1bace..07883266ac73 100644
--- a/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
+++ b/compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
@@ -315,8 +315,12 @@ trait TypeAssigner {
   def assignType(tree: untpd.Select, qual: Tree)(implicit ctx: Context): Select = {
     def qualType = qual.tpe.widen
     def arrayElemType = {
-      val JavaArrayType(elemtp) = qualType
-      elemtp
+      qualType match {
+        case JavaArrayType(elemtp) => elemtp
+        case _ =>
+          ctx.error("Expected Array but was " + qualType.show, tree.sourcePos)
+          defn.NothingType
+      }
     }
     val p = nme.primitive
     val tp = tree.name match {
diff --git a/tests/neg/i4247.scala b/tests/neg/i4247.scala
new file mode 100644
index 000000000000..6a4db932eb84
--- /dev/null
+++ b/tests/neg/i4247.scala
@@ -0,0 +1,3 @@
+class Foo[U] { self : Array[U] & Nothing =>
+  val s = self(0) // error
+}
diff --git a/tests/neg/i4247b.scala b/tests/neg/i4247b.scala
new file mode 100644
index 000000000000..1272fd372e28
--- /dev/null
+++ b/tests/neg/i4247b.scala
@@ -0,0 +1,3 @@
+class Foo[U] { self : Array[U] =>
+  self(0) // error
+}