diff --git a/src/lnm_utils.c b/src/lnm_utils.c
index 849c31f..47989bf 100644
--- a/src/lnm_utils.c
+++ b/src/lnm_utils.c
@@ -59,8 +59,8 @@ uint64_t lnm_digits(uint64_t num) {
 bool lnm_is_ascii(const char *s) {
   bool valid = true;
 
-  while (valid && *s != '\0') {
-    valid = *s < 0;
+  while (valid && (*s != '\0')) {
+    valid = *s >= 0;
 
     s++;
   }