diff --git a/src/dnssec.c b/src/dnssec.c
index f874b61..01b18b9 100644
--- a/src/dnssec.c
+++ b/src/dnssec.c
@@ -1643,7 +1643,7 @@ static int prove_non_existence_nsec3(struct dns_header *header, size_t plen, uns
       if (*closest_encloser == '.')
 	closest_encloser++;
 
-      if (wild_offset != 0 && name - closest_encloser == wild_offset)
+      if (wild_offset != 0 && closest_encloser - name == wild_offset)
 	break;
       
       if (dec_counter(validate_counter, NULL))