diff --git a/mutants/mutant-5/swen90006/machine/Machine.java b/mutants/mutant-5/swen90006/machine/Machine.java
index 9bf57316d1c736ea2bd1c62bd6df3c6c0282f331..4680a6acd2660462c33ec30a29c485963e6b9d81 100644
--- a/mutants/mutant-5/swen90006/machine/Machine.java
+++ b/mutants/mutant-5/swen90006/machine/Machine.java
@@ -235,6 +235,9 @@ public class Machine
 	int rs2 = parseReg(toks[3]);
 	do_div(rd,rs1,rs2);
       } else if (toks[0].equals(INSTRUCTION_RETURN)){
+          if (toks.length != 2){
+	  throw new InvalidInstructionException();
+	}
 	int rs = parseReg(toks[1]);
 	count++;
 	return regs[rs];