diff --git a/mutants/mutant-4/swen90006/machine/Machine.java b/mutants/mutant-4/swen90006/machine/Machine.java
index 9bf57316d1c736ea2bd1c62bd6df3c6c0282f331..5c003b6aa3ce343262f817e230f7446fe22eff65 100644
--- a/mutants/mutant-4/swen90006/machine/Machine.java
+++ b/mutants/mutant-4/swen90006/machine/Machine.java
@@ -1,4 +1,4 @@
-package swen90006.machine;
+package swen90006.machine;
 
 import java.util.Arrays;
 import java.util.List;
@@ -140,7 +140,8 @@ public class Machine
   private void validate_reg(int reg)
     throws InvalidInstructionException
   {
-    if (reg < 0 || reg > MAX_REG) {
+  /* mutation reg==19  */
+    if (reg < 0 || reg > MAX_REG||reg==19) {
       throw new InvalidInstructionException();
     }
   }