diff --git a/compiler/builtins/bitcode/src/num.zig b/compiler/builtins/bitcode/src/num.zig
index bc20195d1d..dd8e00f036 100644
--- a/compiler/builtins/bitcode/src/num.zig
+++ b/compiler/builtins/bitcode/src/num.zig
@@ -22,12 +22,12 @@ pub fn asin(num: f64) callconv(.C) f64 {
     return @call(.{ .modifier = always_inline }, math.asin, .{num});
 }
 
-/// TODO: Obviously, this should not be an alias for arcsin(x);
+/// TODO: Obviously, this should not be an alias for x + 1.
 /// fix me!
-pub fn bytesToU16C(num: f64) callconv(.C) f64 {
+pub fn bytesToU16C(num: usize) callconv(.C) usize {
     return @call(.{ .modifier = always_inline }, bytesToU16, .{num});
 }
 
-fn bytesToU16(num: f64) f64 {
+fn bytesToU16(num: usize) usize {
     return num + 1;
 }
diff --git a/compiler/builtins/src/std.rs b/compiler/builtins/src/std.rs
index ea0b749ae8..9a4611e0f6 100644
--- a/compiler/builtins/src/std.rs
+++ b/compiler/builtins/src/std.rs
@@ -505,8 +505,8 @@ pub fn types() -> MutMap<Symbol, (SolvedType, Region)> {
     // bytesToU16 : Float a -> Float a
     add_top_level_function_type!(
         Symbol::NUM_BYTES_TO_U16,
-        vec![float_type(flex(TVAR1))],
-        Box::new(float_type(flex(TVAR1))),
+        vec![nat_type()],
+        Box::new(nat_type()),
     );
 
     // Bool module
diff --git a/compiler/can/src/builtins.rs b/compiler/can/src/builtins.rs
index da496a36b2..0217440687 100644
--- a/compiler/can/src/builtins.rs
+++ b/compiler/can/src/builtins.rs
@@ -1090,7 +1090,7 @@ fn num_asin(symbol: Symbol, var_store: &mut VarStore) -> Def {
 }
 
 /// TODO: This is obviously wrong! Fix me!
-/// Num.bytesToU16 : Float -> Float
+/// Num.bytesToU16 : Nat -> Nat
 fn num_bytes_to_u16(symbol: Symbol, var_store: &mut VarStore) -> Def {
     let arg_float_var = var_store.fresh();
     let ret_float_var = var_store.fresh();
diff --git a/compiler/test_gen/src/gen_num.rs b/compiler/test_gen/src/gen_num.rs
index 047c9f4e9b..e0acc3f1fa 100644
--- a/compiler/test_gen/src/gen_num.rs
+++ b/compiler/test_gen/src/gen_num.rs
@@ -1623,11 +1623,11 @@ mod gen_num {
 
     #[test]
     fn num_bytes_to_u16_ascii() {
-        assert_evals_to!("Num.bytesToU16 1", 2.0, f64);
+        assert_evals_to!("Num.bytesToU16 1", 2, usize);
     }
 
     #[test]
     fn num_bytes_to_u16_ascii_2() {
-        assert_evals_to!("Num.bytesToU16 0", 1.0, f64);
+        assert_evals_to!("Num.bytesToU16 0", 1, usize);
     }
 }