diff --git a/fmt_asn1tag.c b/fmt_asn1tag.c
index 8189cae..8fa1605 100644
--- a/fmt_asn1tag.c
+++ b/fmt_asn1tag.c
@@ -4,7 +4,7 @@
 /* as used in ASN.1 tags */
 size_t fmt_asn1tag(char* dest,enum asn1_tagclass tc,enum asn1_tagtype tt,unsigned long l) {
   /* encoding is either l%128 or (0x1f,...) */
-  size_t needed=(sizeof l)*7/8,i;
+  size_t needed=((sizeof l)*7)/8,i;
   if (l<0x1f) {
     if (dest) *dest=(int)tc+(int)tt+(l&0x1f);
     return 1;