diff --git a/src/main/wacc/backend/asmGenerator.scala b/src/main/wacc/backend/asmGenerator.scala
index db2e694..500d398 100644
--- a/src/main/wacc/backend/asmGenerator.scala
+++ b/src/main/wacc/backend/asmGenerator.scala
@@ -174,7 +174,7 @@ object asmGenerator {
             asm ++= evalExprOntoStack(rhs)
             asm ++= evalExprOntoStack(i)
             asm += stack.pop(RCX)
-            asm += Compare(ECX, ImmediateVal(0))
+            asm += Compare(RCX, ImmediateVal(0))
             asm += Jump(labelGenerator.getLabelArg(OutOfBoundsError), Cond.Less)
             asm += stack.push(KnownType.Int.size, RCX)
             asm ++= evalExprOntoStack(x)
@@ -461,8 +461,8 @@ object asmGenerator {
 
   def stackAlign: AsmLine = And(Register(Size.Q64, SP), ImmediateVal(-16))
   private def zeroRest(dest: Dest, size: Size): Chain[AsmLine] = size match {
-    case Size.Q64 | Size.D32 => Chain.empty
-    case _                   => Chain.one(And(dest, ImmediateVal((1 << (size.toInt * 8)) - 1)))
+    case Size.Q64 => Chain.empty
+    case _        => Chain.one(And(dest, ImmediateVal(((BigInt(1) << (size.toInt * 8)) - 1).toInt)))
   }
 
   private val escapedCharsMapping = escapedChars.map { case (k, v) => v -> s"\\$k" }