diff --git a/src/shared/watchdog.c b/src/shared/watchdog.c
index f29d3761b0..98ef979dbe 100644
--- a/src/shared/watchdog.c
+++ b/src/shared/watchdog.c
@@ -20,6 +20,20 @@ static char *watchdog_device;
 static usec_t watchdog_timeout; /* 0 → close device and USEC_INFINITY → don't change timeout */
 static usec_t watchdog_last_ping = USEC_INFINITY;
 
+/* Starting from kernel version 4.5, the maximum allowable watchdog timeout is
+ * UINT_MAX/1000U seconds (since internal calculations are done in milliseconds
+ * using unsigned integers. However, the kernel's userspace API for the watchdog
+ * uses signed integers for its ioctl parameters (even for timeout values and
+ * bit flags) so this is why we must consider the maximum signed integer value
+ * as well.
+ */
+#define WATCHDOG_TIMEOUT_MAX_SEC (CONST_MIN(UINT_MAX/1000U, (unsigned)INT_MAX))
+
+static int saturated_usec_to_sec(usec_t val) {
+        usec_t t = DIV_ROUND_UP(val, USEC_PER_SEC);
+        return MIN(t, (usec_t) WATCHDOG_TIMEOUT_MAX_SEC); /* Saturate to watchdog max */
+}
+
 static int watchdog_set_enable(bool enable) {
         int flags = enable ? WDIOS_ENABLECARD : WDIOS_DISABLECARD;
 
@@ -54,14 +68,12 @@ static int watchdog_get_timeout(void) {
 }
 
 static int watchdog_set_timeout(void) {
-        usec_t t;
         int sec;
 
         assert(watchdog_fd >= 0);
         assert(timestamp_is_set(watchdog_timeout));
 
-        t = DIV_ROUND_UP(watchdog_timeout, USEC_PER_SEC);
-        sec = MIN(t, (usec_t) INT_MAX); /* Saturate */
+        sec = saturated_usec_to_sec(watchdog_timeout);
 
         if (ioctl(watchdog_fd, WDIOC_SETTIMEOUT, &sec) < 0)
                 return -errno;