diff --git a/src/libsystemd-id128/sd-id128.c b/src/libsystemd-id128/sd-id128.c
index 4286ae7d14..68c4987149 100644
--- a/src/libsystemd-id128/sd-id128.c
+++ b/src/libsystemd-id128/sd-id128.c
@@ -170,6 +170,9 @@ _public_ int sd_id128_get_boot(sd_id128_t *ret) {
         for (j = 0, p = buf; j < 16; j++) {
                 int a, b;
 
+                if (p >= buf + k)
+                        return -EIO;
+
                 if (*p == '-')
                         p++;