1 files changed, 3 insertions, 1 deletions

diff --git a/lib/libc/stdlib/strtoull.c b/lib/libc/stdlib/strtoull.c
index ee1e13b7d7c2..16dda0be3971 100644
--- a/lib/libc/stdlib/strtoull.c
+++ b/lib/libc/stdlib/strtoull.c
@@ -56,7 +56,7 @@ strtouq(nptr, endptr, base)
 {
 	register const char *s = nptr;
 	register u_quad_t acc;
-	register int c;
+	register unsigned char c;
 	register u_quad_t qbase, cutoff;
 	register int neg, any, cutlim;
 
@@ -87,6 +87,8 @@ strtouq(nptr, endptr, base)
 	cutoff = (u_quad_t)UQUAD_MAX / qbase;
 	cutlim = (u_quad_t)UQUAD_MAX % qbase;
 	for (acc = 0, any = 0;; c = *s++) {
+		if (!isascii(c))
+			break;
 		if (isdigit(c))
 			c -= '0';
 		else if (isalpha(c))