diff --git a/mutants/mutant-4/swen90006/machine/Machine.java b/mutants/mutant-4/swen90006/machine/Machine.java
index 9bf57316d1c736ea2bd1c62bd6df3c6c0282f331..3be531691a72e412dce6859b2319c7c6807850bd 100644
--- a/mutants/mutant-4/swen90006/machine/Machine.java
+++ b/mutants/mutant-4/swen90006/machine/Machine.java
@@ -217,7 +217,7 @@ public class Machine
 	int rd = parseReg(toks[1]);
 	int rs1 = parseReg(toks[2]);
 	int rs2 = parseReg(toks[3]);
-	do_sub(rd,rs1,rs2);
+	do_add(rd,rs1,rs2);
       } else if (toks[0].equals(INSTRUCTION_MULT)){
 	if (toks.length != 4){
 	  throw new InvalidInstructionException();