cast fixes undefined behaviour; closes #1919 in upstream

diff --git a/vm/layouts.hpp b/vm/layouts.hpp
index 7975f4ca92c1c5c8a8257e40d96d0102cb1e1de8..e60201ed5dd7a9b3f98fbaf73d6daead50231c44 100644 (file)
--- a/vm/layouts.hpp
+++ b/vm/layouts.hpp
@@ -104,7 +104,7 @@ inline static fixnum untag_fixnum(cell tagged) {
 }
 
 inline static cell tag_fixnum(fixnum untagged) {
-  return (untagged << TAG_BITS) | FIXNUM_TYPE;
+  return ( (cell)untagged << TAG_BITS) | FIXNUM_TYPE;
 }
 
 #define NO_TYPE_CHECK static const cell type_number = TYPE_COUNT