diff --git a/contrib/untar.c b/contrib/untar.c
index 6d5e88e2..0d862b8a 100644
--- a/contrib/untar.c
+++ b/contrib/untar.c
@@ -60,11 +60,11 @@ parseoct(const char *p, size_t n)
 {
 	unsigned long i = 0;
 
-	while ((*p < '0' || *p > '7') && n > 0) {
+	while (n > 0 && (*p < '0' || *p > '7')) {
 		++p;
 		--n;
 	}
-	while (*p >= '0' && *p <= '7' && n > 0) {
+	while (n > 0 && *p >= '0' && *p <= '7') {
 		i *= 8;
 		i += *p - '0';
 		++p;