1 files changed, 16 insertions, 0 deletions
diff --git a/src/dotty/tools/dotc/typer/RefChecks.scala b/src/dotty/tools/dotc/typer/RefChecks.scala
index 2b81af5cb..f45966741 100644
--- a/src/dotty/tools/dotc/typer/RefChecks.scala
+++ b/src/dotty/tools/dotc/typer/RefChecks.scala
@@ -814,6 +814,22 @@ class RefChecks extends MiniPhase with SymTransformer { thisTransformer =>
       currentLevel.enterReference(tree.tpe.typeSymbol, tree.pos)
       tree
     }
+
+    override def transformTypeApply(tree: tpd.TypeApply)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
+      tree.fun match {
+        case fun@Select(qual, selector) =>
+          val sym = tree.symbol
+
+          if (sym == defn.Any_isInstanceOf) {
+            val argType = tree.args.head.tpe
+            val qualCls = qual.tpe.widen.classSymbol
+            val argCls = argType.classSymbol
+            if (qualCls.isPrimitiveValueClass && !argCls.isPrimitiveValueClass) ctx.error("isInstanceOf cannot test if value types are references", tree.pos)
+          }
+        case _ =>
+      }
+      tree
+    }
   }
 }