diff --git a/basis/struct-vectors/struct-vectors.factor b/basis/struct-vectors/struct-vectors.factor
index 974fa1d452..b29ab19e4d 100644
--- a/basis/struct-vectors/struct-vectors.factor
+++ b/basis/struct-vectors/struct-vectors.factor
@@ -12,6 +12,7 @@ TUPLE: struct-vector
 : <struct-vector> ( capacity c-type -- struct-vector )
     [ <struct-array> 0 ] keep struct-vector boa ; inline
 
+M: struct-vector byte-length underlying>> byte-length ;
 M: struct-vector new-sequence
     [ c-type>> <struct-array> ] [ [ >fixnum ] [ c-type>> ] bi* ] 2bi
     struct-vector boa ;