diff --git a/src/shared/hostname-setup.c b/src/shared/hostname-setup.c
index 42a8ada144..19e528604b 100644
--- a/src/shared/hostname-setup.c
+++ b/src/shared/hostname-setup.c
@@ -22,7 +22,7 @@ static int sethostname_idempotent_full(const char *s, bool really) {
 
         assert(s);
 
-        if (gethostname(buf, sizeof(buf)) < 0)
+        if (gethostname(buf, sizeof(buf) - 1) < 0)
                 return -errno;
 
         if (streq(buf, s))