diff --git a/src/main/scala/Parser.scala b/src/main/scala/Parser.scala
index 8a8ee44e..fbe9aa8a 100644
--- a/src/main/scala/Parser.scala
+++ b/src/main/scala/Parser.scala
@@ -98,18 +98,18 @@ case class Parser(input: String) {
     positioned(
       P(
         "0" | "-".? ~ (CharIn("1-9") ~ CharsWhileIn("0-9").?)
-      ).!.map((n: String) => EInt(n.toInt)).opaque("integer")
+      ).!.map((n: String) => EInt(BigInt(n))).opaque("integer")
     )
   def hex[K: P]: P[Expr] =
     positioned(
       P("0x" ~/ CharIn("0-9a-fA-F").rep(1)).!.map((n: String) =>
-        EInt(Integer.parseInt(n.substring(2), 16), 16)
+        EInt(BigInt(n.substring(2), 16), 16)
       ).opaque("hexademical")
     )
   def octal[K: P]: P[Expr] =
     positioned(
       P("0" ~ CharsWhileIn("0-7")).!.map((n: String) =>
-        EInt(Integer.parseInt(n.substring(1), 8), 8)
+        EInt(BigInt(n.substring(1), 8), 8)
       ).opaque("ocatal")
     )
   def rational[K: P]: P[Expr] =
diff --git a/src/main/scala/Utils.scala b/src/main/scala/Utils.scala
index 71195380..94eebc13 100644
--- a/src/main/scala/Utils.scala
+++ b/src/main/scala/Utils.scala
@@ -1,6 +1,6 @@
 package fuselang
 import scala.{PartialFunction => PF}
-import scala.math.{log10, ceil, abs}
+import scala.math.{log10, ceil}
 
 object Utils {
 
@@ -11,10 +11,22 @@ object Utils {
     }
   }
 
+  // https://codereview.stackexchange.com/questions/14561/matching-bigints-in-scala
+  // TODO: This can overflow and result in an runtime exception
+  object Big {
+    def unapply(n: BigInt) = Some(n.toInt)
+  }
+
   def bitsNeeded(n: Int): Int = n match {
     case 0 => 1
     case n if n > 0 => ceil(log10(n + 1) / log10(2)).toInt
-    case n if n < 0 => bitsNeeded(abs(n)) + 1
+    case n if n < 0 => bitsNeeded(n.abs) + 1
+  }
+
+  def bitsNeeded(n: BigInt): Int = n match {
+    case Big(0) => 1
+    case n if n > 0 => ceil(log10((n + 1).toDouble) / log10(2)).toInt
+    case n if n < 0 => bitsNeeded(n.abs) + 1
   }
 
   def cartesianProduct[T](llst: Seq[Seq[T]]): Seq[Seq[T]] = {
diff --git a/src/main/scala/backends/CppLike.scala b/src/main/scala/backends/CppLike.scala
index 7034f8b3..8a92638e 100644
--- a/src/main/scala/backends/CppLike.scala
+++ b/src/main/scala/backends/CppLike.scala
@@ -82,10 +82,10 @@ object Cpp {
 
     implicit def IdToString(id: Id): Doc = value(id.v)
 
-    def emitBaseInt(v: Int, base: Int): String = base match {
-      case 8 => s"0${Integer.toString(v, 8)}"
+    def emitBaseInt(v: BigInt, base: Int): String = base match {
+      case 8 => s"0${v.toString(8)}"
       case 10 => v.toString
-      case 16 => s"0x${Integer.toString(v, 16)}"
+      case 16 => s"0x${v.toString(16)}"
     }
 
     implicit def emitExpr(e: Expr): Doc = e match {
diff --git a/src/main/scala/common/CodeGenHelpers.scala b/src/main/scala/common/CodeGenHelpers.scala
index 095c7a50..77382c94 100644
--- a/src/main/scala/common/CodeGenHelpers.scala
+++ b/src/main/scala/common/CodeGenHelpers.scala
@@ -1,5 +1,7 @@
 package fuselang.common
 
+import fuselang.Utils.Big
+
 import scala.math.log10
 
 object CodeGenHelpers {
@@ -35,10 +37,10 @@ object CodeGenHelpers {
   }
 
   // Using the trick defined here: https://www.geeksforgeeks.org/program-to-find-whether-a-no-is-power-of-two/
-  def isPowerOfTwo(x: Int) =
+  def isPowerOfTwo(x: BigInt) =
     x != 0 && ((x & (x - 1)) == 0)
 
-  def log2(n: Int) = log10(n) / log10(2)
+  def log2(n: BigInt) = log10(n.toDouble) / log10(2)
 
   def fastDiv(l: Expr, r: Expr) = (l, r) match {
     case (EInt(n, b), EInt(m, _)) => EInt(n / m, b)
@@ -68,14 +70,14 @@ object CodeGenHelpers {
 
   // Simple peephole optimization to turn: 1 * x => x, 0 + x => x, 0 * x => 0
   def binop(op: BOp, l: Expr, r: Expr) = (op, l, r) match {
-    case (NumOp("*", _), EInt(1, _), r) => r
-    case (NumOp("*", _), l, EInt(1, _)) => l
-    case (NumOp("*", _), EInt(0, b), _) => EInt(0, b)
-    case (NumOp("*", _), _, EInt(0, b)) => EInt(0, b)
-    case (NumOp("+", _), l, EInt(0, _)) => l
-    case (NumOp("+", _), EInt(0, _), r) => r
-    case (BitOp("<<"), l, EInt(0, _)) => l
-    case (BitOp(">>"), l, EInt(0, _)) => l
+    case (NumOp("*", _), EInt(Big(1), _), r) => r
+    case (NumOp("*", _), l, EInt(Big(1), _)) => l
+    case (NumOp("*", _), EInt(Big(0), b), _) => EInt(0, b)
+    case (NumOp("*", _), _, EInt(Big(0), b)) => EInt(0, b)
+    case (NumOp("+", _), l, EInt(Big(0), _)) => l
+    case (NumOp("+", _), EInt(Big(0), _), r) => r
+    case (BitOp("<<"), l, EInt(Big(0), _)) => l
+    case (BitOp(">>"), l, EInt(Big(0), _)) => l
     case _ => EBinop(op, l, r)
   }
 
diff --git a/src/main/scala/common/Errors.scala b/src/main/scala/common/Errors.scala
index 77ca72da..162110fa 100644
--- a/src/main/scala/common/Errors.scala
+++ b/src/main/scala/common/Errors.scala
@@ -97,7 +97,7 @@ object Errors {
         pos
       )
 
-  case class IndexOutOfBounds(id: Id, size: Int, mv: Int, pos: Position)
+  case class IndexOutOfBounds(id: Id, size: BigInt, mv: BigInt, pos: Position)
       extends TypeError(
         s"Index out of bounds for `$id'. Memory size is $size, iterator max val is $mv",
         pos
diff --git a/src/main/scala/common/Pretty.scala b/src/main/scala/common/Pretty.scala
index 4bd5d910..e74bd4b1 100644
--- a/src/main/scala/common/Pretty.scala
+++ b/src/main/scala/common/Pretty.scala
@@ -59,10 +59,10 @@ object Pretty {
 
   def emitTyp(t: Type): Doc = text(t.toString)
 
-  def emitBaseInt(v: Int, base: Int): String = base match {
-    case 8 => s"0${Integer.toString(v, 8)}"
+  def emitBaseInt(v: BigInt, base: Int): String = base match {
+    case 8 => s"0${v.toString(8)}"
     case 10 => v.toString
-    case 16 => s"0x${Integer.toString(v, 16)}"
+    case 16 => s"0x${v.toString(16)}"
   }
 
   implicit def emitExpr(e: Expr)(implicit debug: Boolean): Doc = e match {
diff --git a/src/main/scala/common/Syntax.scala b/src/main/scala/common/Syntax.scala
index 8f0b1158..ebf986ea 100644
--- a/src/main/scala/common/Syntax.scala
+++ b/src/main/scala/common/Syntax.scala
@@ -81,7 +81,7 @@ object Syntax {
   // Types that can be upcast to Ints
   sealed trait IntType
   case class TSizedInt(len: Int, unsigned: Boolean) extends Type with IntType
-  case class TStaticInt(v: Int) extends Type with IntType
+  case class TStaticInt(v: BigInt) extends Type with IntType
   case class TIndex(static: (Int, Int), dynamic: (Int, Int))
       extends Type
       with IntType {
@@ -135,7 +135,7 @@ object Syntax {
       case _ => false
     }
   }
-  case class EInt(v: Int, base: Int = 10) extends Expr
+  case class EInt(v: BigInt, base: Int = 10) extends Expr
   case class ERational(d: String) extends Expr
   case class EBool(v: Boolean) extends Expr
   case class EBinop(op: BOp, e1: Expr, e2: Expr) extends Expr
diff --git a/src/main/scala/passes/BoundsCheck.scala b/src/main/scala/passes/BoundsCheck.scala
index a73cad0a..4e19d355 100644
--- a/src/main/scala/passes/BoundsCheck.scala
+++ b/src/main/scala/passes/BoundsCheck.scala
@@ -35,7 +35,7 @@ object BoundsChecker {
           case Rotation(e) => (e, 1)
         }
 
-        val maxVal: Int =
+        val maxVal: BigInt =
           sufExpr.typ
             .getOrThrow(Impossible(s"$sufExpr is missing type"))
             .matchOrError(viewId.pos, "view", "Integer Type") {
diff --git a/src/main/scala/passes/LowerUnroll.scala b/src/main/scala/passes/LowerUnroll.scala
index b8e28460..fbe361a4 100644
--- a/src/main/scala/passes/LowerUnroll.scala
+++ b/src/main/scala/passes/LowerUnroll.scala
@@ -270,7 +270,7 @@ object LowerUnroll extends PartialTransformer {
       .map({
         case ((_, bank), idx) =>
           idx match {
-            case EInt(n, 10) => Some(n % bank)
+            case EInt(n, 10) => Some((n % bank).toInt)
             case EInt(_, _) =>
               throw NotImplemented(
                 "Indexing using non decimal integers",
diff --git a/src/main/scala/typechecker/AffineCheck.scala b/src/main/scala/typechecker/AffineCheck.scala
index fd3a88e4..b8e8b0b0 100644
--- a/src/main/scala/typechecker/AffineCheck.scala
+++ b/src/main/scala/typechecker/AffineCheck.scala
@@ -144,7 +144,7 @@ object AffineChecker {
                 (bres * (e - s), Range(s, e) +: consume)
             // Index is a statically known number.
             case TStaticInt(v) =>
-              (bres * 1, Seq(v % dims(dim)._2) +: consume)
+              (bres * 1, Seq((v % dims(dim)._2).toInt) +: consume)
             // Index is a dynamic number.
             case _: TSizedInt =>
               if (dims(dim)._2 != 1)
diff --git a/src/main/scala/typechecker/Subtyping.scala b/src/main/scala/typechecker/Subtyping.scala
index 58bd0da0..54782a04 100644
--- a/src/main/scala/typechecker/Subtyping.scala
+++ b/src/main/scala/typechecker/Subtyping.scala
@@ -99,7 +99,7 @@ object Subtyping {
         Some(TSizedInt(max(s, bitsNeeded(v)), un))
       case (st: TStaticInt, idx: TIndex) =>
         // Infer unsigned
-        Some(TSizedInt(bitsNeeded(max(idx.maxVal, st.v)), false))
+        Some(TSizedInt(bitsNeeded(st.v.max(idx.maxVal)), false))
       case (t2: TSizedInt, _: TIndex) => Some(t2)
       case (_: TFloat, _: TDouble) => Some(TDouble())
       case (_: TRational, _: TFloat) => Some(TFloat())
diff --git a/src/test/scala/ParsingPositive.scala b/src/test/scala/ParsingPositive.scala
index 3aa9615e..49a53241 100644
--- a/src/test/scala/ParsingPositive.scala
+++ b/src/test/scala/ParsingPositive.scala
@@ -9,6 +9,7 @@ class ParsingTests extends org.scalatest.FunSuite {
     parseAst("0.25;")
     parseAst("0x19;")
     parseAst("014;")
+    parseAst("0x9e3779b9;")
   }
 
   test("atoms") {
diff --git a/src/test/scala/TypeCheckerSpec.scala b/src/test/scala/TypeCheckerSpec.scala
index 4ee9827e..507b4cda 100644
--- a/src/test/scala/TypeCheckerSpec.scala
+++ b/src/test/scala/TypeCheckerSpec.scala
@@ -31,6 +31,12 @@ class TypeCheckerSpec extends FunSpec {
           typeCheck("let x: fix<2,2> = 2+2.1;")
         }
       }
+      it("should allow large unsigned literals") {
+        typeCheck("let x: ubit<32> = 0x9e3779b9;")
+        typeCheck("let x: ubit<64> = 0xffffffffffffffff;")
+        typeCheck("let x: bit<64> = 0x7fffffffffffffff;")
+        typeCheck("let x: ubit<128> = 0xffffffffffffffffffffffffffffffff;")
+      }
     }
 
     describe("with explicit type and without initializer") {
@@ -231,6 +237,9 @@ class TypeCheckerSpec extends FunSpec {
     it("result of fix type addition upcast to subtype join") {
       typeCheck("decl x: fix<32,16>; decl y: fix<16,8>; let z = x + y;")
     }
+    it("result of peephole optimization on large unsigned int should be valid") {
+      typeCheck("let x: ubit<32> = 0x9e3779b9; let y = x + 0;")
+    }
   }
 
   describe("Reassign") {