diff --git a/builtin/builtin.mbti b/builtin/builtin.mbti
index a2eff4a1a..6ae548486 100644
--- a/builtin/builtin.mbti
+++ b/builtin/builtin.mbti
@@ -644,6 +644,7 @@ impl Double {
   to_int(Double) -> Int
   to_int64(Double) -> Int64
   to_json(Double) -> Json
+  to_uint64(Double) -> UInt64
   until(Double, Double, step~ : Double = .., inclusive~ : Bool = ..) -> Iter[Double]
   upto(Double, Double, inclusive~ : Bool = ..) -> Iter[Double] //deprecated
 }
diff --git a/double/double.mbti b/double/double.mbti
index 654ec9c25..a49f75a0c 100644
--- a/double/double.mbti
+++ b/double/double.mbti
@@ -40,6 +40,7 @@ impl Double {
   to_be_bytes(Double) -> Bytes
   to_le_bytes(Double) -> Bytes
   to_string(Double) -> String
+  to_uint(Double) -> UInt
   trunc(Double) -> Double
 }