diff --git a/src/libudev/libudev-monitor.c b/src/libudev/libudev-monitor.c
index 484fefeebfe..0d361426f7c 100644
--- a/src/libudev/libudev-monitor.c
+++ b/src/libudev/libudev-monitor.c
@@ -609,7 +609,7 @@ retry:
                 return NULL;
         }
 
-        if (buflen < 32 || (size_t)buflen >= sizeof(buf)) {
+        if (buflen < 32 || (smsg.msg_flags & MSG_TRUNC)) {
                 log_debug("invalid message length");
                 return NULL;
         }