diff --git a/libguile/gc.c b/libguile/gc.c
index e2a09ccc9..6e77235f7 100644
--- a/libguile/gc.c
+++ b/libguile/gc.c
@@ -1113,7 +1113,7 @@ scm_gc_sweep ()
 		if ((SCM_CDR (vcell) == 0) || (SCM_CDR (vcell) == 1))
 		  {
 		    SCM *p = (SCM *) SCM_GCCDR (scmptr);
- 		    m += p[scm_struct_i_n_words] * sizeof (SCM);
+ 		    m += (p[scm_struct_i_n_words] + 7) * sizeof (SCM);
 		    /* I feel like I'm programming in BCPL here... */
 		    free ((char *) p[scm_struct_i_ptr]);
 		  }