diff --git a/library/compiler-builtins/testcrate/build.rs b/library/compiler-builtins/testcrate/build.rs
index 0fa2f5631b9a..292d36a77ac8 100644
--- a/library/compiler-builtins/testcrate/build.rs
+++ b/library/compiler-builtins/testcrate/build.rs
@@ -777,7 +777,7 @@ fn main() {
     }
     
     // count leading zeros
-    gen(|a: MyU128| {
+    gen(|a: MyU64| {
             Some((a as usize).leading_zeros())
         },
         "{