diff --git a/libc/src/__support/UInt.h b/libc/src/__support/UInt.h
--- a/libc/src/__support/UInt.h
+++ b/libc/src/__support/UInt.h
@@ -116,7 +116,7 @@
         return lo;
       }
     } else {
-      return (static_cast<T>(val[1]) << 64) + lo;
+      return static_cast<T>((static_cast<T>(val[1]) << 64) + lo);
     }
   }