diff --git a/gnovm/pkg/gnolang/preprocess.go b/gnovm/pkg/gnolang/preprocess.go
index 459910505b9..88c5c2f1da4 100644
--- a/gnovm/pkg/gnolang/preprocess.go
+++ b/gnovm/pkg/gnolang/preprocess.go
@@ -2477,7 +2477,7 @@ func checkOrConvertType(store Store, last BlockNode, x *Expr, t Type, autoNative
 		// convert type
 		if isUntyped(xt) { // convert if x is untyped literal
 			if t == nil {
-				t = defaultTypeOf(xt)
+				t = defaultTypeOf(xt, nil)
 			}
 			// Push type into expr if qualifying binary expr.
 			if bx, ok := (*x).(*BinaryExpr); ok {
diff --git a/gnovm/pkg/gnolang/types.go b/gnovm/pkg/gnolang/types.go
index fcfcd7d9d37..86b3d588eda 100644
--- a/gnovm/pkg/gnolang/types.go
+++ b/gnovm/pkg/gnolang/types.go
@@ -1203,8 +1203,8 @@ func (ft *FuncType) Specify(store Store, argTVs []TypedValue, isVarg bool) *Func
 					continue
 				} else if vargt == nil {
 					vargt = varg.T
-				} else if isUntyped(varg.T) && vargt.TypeID() == defaultTypeOf(varg.T).TypeID() {
-					vargt = defaultTypeOf(varg.T)
+				} else if isUntyped(varg.T) && vargt.TypeID() == defaultTypeOf(varg.T, varg.V).TypeID() {
+					vargt = defaultTypeOf(varg.T, varg.V)
 				} else if vargt.TypeID() != varg.T.TypeID() {
 					panic(fmt.Sprintf(
 						"incompatible varg types: expected %v, got %s",
@@ -2281,14 +2281,23 @@ func isDataByte(t Type) bool {
 
 // TODO move untyped const stuff to preprocess.go.
 // TODO associate with ConvertTo() in documentation.
-func defaultTypeOf(t Type) Type {
+func defaultTypeOf(t Type, v Value) Type {
 	switch t {
 	case UntypedBoolType:
 		return BoolType
 	case UntypedRuneType:
 		return Int32Type
 	case UntypedBigintType:
-		return IntType
+		typeVal := IntType
+		if bigintValue, ok := v.(BigintValue); ok {
+			if bigintValue.V != nil && bigintValue.V.Sign() == 1 && !bigintValue.V.IsInt64() {
+				// Use an unsigned type if the value is positive and we know
+				// it won't fit in an int64.
+				typeVal = Uint64Type
+			}
+		}
+
+		return typeVal
 	case UntypedBigdecType:
 		return Float64Type
 	case UntypedStringType:
@@ -2514,7 +2523,7 @@ func specifyType(store Store, lookup map[Name]Type, tmpl Type, spec Type, specTy
 					return // ok
 				} else {
 					if isUntyped(spec) {
-						spec = defaultTypeOf(spec)
+						spec = defaultTypeOf(spec, nil)
 					}
 					lookup[ct.Generic] = spec
 					return // ok
diff --git a/gnovm/pkg/gnolang/values.go b/gnovm/pkg/gnolang/values.go
index b0996b98b6f..d8d4bc58bc3 100644
--- a/gnovm/pkg/gnolang/values.go
+++ b/gnovm/pkg/gnolang/values.go
@@ -1594,7 +1594,7 @@ func (tv *TypedValue) Assign(alloc *Allocator, tv2 TypedValue, cu bool) {
 	}
 	*tv = tv2.Copy(alloc)
 	if cu && isUntyped(tv.T) {
-		ConvertUntypedTo(tv, defaultTypeOf(tv.T))
+		ConvertUntypedTo(tv, defaultTypeOf(tv.T, tv.V))
 	}
 }
 
diff --git a/gnovm/pkg/gnolang/values_conversions.go b/gnovm/pkg/gnolang/values_conversions.go
index b4888878c7a..edaa8883819 100644
--- a/gnovm/pkg/gnolang/values_conversions.go
+++ b/gnovm/pkg/gnolang/values_conversions.go
@@ -926,7 +926,7 @@ func ConvertUntypedTo(tv *TypedValue, t Type) {
 	}
 	// general case
 	if t == nil {
-		t = defaultTypeOf(tv.T)
+		t = defaultTypeOf(tv.T, tv.V)
 	}
 	switch tv.T {
 	case UntypedBoolType:
diff --git a/gnovm/tests/files/bigint1.gno b/gnovm/tests/files/bigint1.gno
new file mode 100644
index 00000000000..01032e27b3f
--- /dev/null
+++ b/gnovm/tests/files/bigint1.gno
@@ -0,0 +1,14 @@
+package main
+
+import (
+	"math"
+)
+
+func main() {
+	println(float64(math.MaxUint32))
+	println(float64(math.MaxUint64))
+}
+
+// Output:
+// 4.294967295e+09
+// 1.8446744073709552e+19