diff --git a/servers/slapd/extended.c b/servers/slapd/extended.c
index e77f7c6a4e..072b9f0205 100644
--- a/servers/slapd/extended.c
+++ b/servers/slapd/extended.c
@@ -416,10 +416,10 @@ whoami_extop (
 
 	bv = (struct berval *) ch_malloc( sizeof(struct berval) );
 	if( op->o_dn.bv_len ) {
-		bv->bv_len = op->o_dn.bv_len + sizeof("dn:")-1;
+		bv->bv_len = op->o_dn.bv_len + STRLENOF( "dn:" );
 		bv->bv_val = ch_malloc( bv->bv_len + 1 );
-		AC_MEMCPY( bv->bv_val, "dn:", sizeof("dn:")-1 );
-		AC_MEMCPY( &bv->bv_val[sizeof("dn:")-1], op->o_dn.bv_val,
+		AC_MEMCPY( bv->bv_val, "dn:", STRLENOF( "dn:" ) );
+		AC_MEMCPY( &bv->bv_val[STRLENOF( "dn:" )], op->o_dn.bv_val,
 			op->o_dn.bv_len );
 		bv->bv_val[bv->bv_len] = '\0';