diff --git a/src/main/wacc/backend/RuntimeError.scala b/src/main/wacc/backend/RuntimeError.scala
index e6e972c..934077a 100644
--- a/src/main/wacc/backend/RuntimeError.scala
+++ b/src/main/wacc/backend/RuntimeError.scala
@@ -3,6 +3,8 @@ package wacc
 import cats.data.Chain
 import wacc.assemblyIR._
 
+val ERROR_CODE = 255
+
 sealed trait RuntimeError {
   def strLabel: String
   def errStr: String
@@ -33,7 +35,7 @@ object RuntimeError {
   // private val RBP = Register(Q64, BP)
   private val RSI = Register(Q64, SI)
   // private val RDX = Register(Q64, DX)
-  // private val RCX = Register(Q64, CX)
+  private val RCX = Register(Q64, CX)
 
   case object ZeroDivError extends RuntimeError {
     val strLabel = ".L._errDivZero_str0"
@@ -62,7 +64,7 @@ object RuntimeError {
       stackAlign,
       Load(RDI, IndexAddress(RIP, LabelArg(BadChrError.strLabel))),
       assemblyIR.Call(CLibFunc.PrintF),
-      Move(RDI, ImmediateVal(255)),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
       assemblyIR.Call(CLibFunc.Exit)
     )
 
@@ -78,7 +80,7 @@ object RuntimeError {
       stackAlign,
       Load(RDI, IndexAddress(RIP, LabelArg(NullPtrError.strLabel))),
       assemblyIR.Call(CLibFunc.PrintF),
-      Move(RDI, ImmediateVal(255)),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
       assemblyIR.Call(CLibFunc.Exit)
     )
 
@@ -94,7 +96,7 @@ object RuntimeError {
       stackAlign,
       Load(RDI, IndexAddress(RIP, LabelArg(OverflowError.strLabel))),
       assemblyIR.Call(CLibFunc.PrintF),
-      Move(RDI, ImmediateVal(255)),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
       assemblyIR.Call(CLibFunc.Exit)
     )
 
@@ -108,11 +110,11 @@ object RuntimeError {
 
     def generateHandler: Chain[AsmLine] = Chain(
       LabelDef(OutOfBoundsError.errLabel),
-      Move(RSI, Register(Q64, CX)),
+      Move(RSI, RCX),
       stackAlign,
       Load(RDI, IndexAddress(RIP, LabelArg(OutOfBoundsError.strLabel))),
       assemblyIR.Call(CLibFunc.PrintF),
-      Move(RDI, ImmediateVal(255)),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
       assemblyIR.Call(CLibFunc.Exit)
     )
   }
@@ -127,7 +129,7 @@ object RuntimeError {
       stackAlign,
       Load(RDI, IndexAddress(RIP, LabelArg(OutOfMemoryError.strLabel))),
       assemblyIR.Call(CLibFunc.PrintF),
-      Move(RDI, ImmediateVal(255)),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
       assemblyIR.Call(CLibFunc.Exit)
     )
   }