diff --git a/sys/posix/strings.c b/sys/posix/strings.c
index e80bad3e2a..03136f2a0b 100644
--- a/sys/posix/strings.c
+++ b/sys/posix/strings.c
@@ -18,7 +18,7 @@
 int strncasecmp(const char *s1, const char *s2, size_t n)
 {
     while (n-- && tolower((unsigned char) *s1) == tolower((unsigned char) *s2)) {
-        if (!n && !*s1) {
+        if (!n || !*s1) {
             break;
         }