diff --git a/nest/rt-attr.c b/nest/rt-attr.c
index 94b105d7..b553475a 100644
--- a/nest/rt-attr.c
+++ b/nest/rt-attr.c
@@ -403,6 +403,7 @@ ea_format(eattr *e, byte *buf)
 	  bsprintf(buf, "%u", e->u.data);
 	  break;
 	case EAF_TYPE_OPAQUE:
+	  *buf = 0;
 	  for(i=0; i<ad->length; i++)
 	    {
 	      if (buf > end - 8)