diff --git a/src/core/core-util.c b/src/core/core-util.c
index dd09ef777..cdf041742 100644
--- a/src/core/core-util.c
+++ b/src/core/core-util.c
@@ -773,9 +773,10 @@ util_parse_delay (const char *string_delay, unsigned long long default_factor,
     if (!str_number)
         return 0;
 
+    errno = 0;
     error = NULL;
     *delay = strtoull (str_number, &error, 10);
-    if (!error || error[0])
+    if ((errno == ERANGE) || !error || error[0])
     {
         free (str_number);
         *delay = 0;
diff --git a/tests/unit/core/test-core-util.cpp b/tests/unit/core/test-core-util.cpp
index 05ad9143d..7e0c40dda 100644
--- a/tests/unit/core/test-core-util.cpp
+++ b/tests/unit/core/test-core-util.cpp
@@ -698,6 +698,7 @@ TEST(CoreUtil, GetTimeDiff)
 TEST(CoreUtil, ParseDelay)
 {
     unsigned long long delay;
+    char str_delay[128];
 
     /* error: no delay */
     LONGS_EQUAL(0, util_parse_delay ("123", 1ULL, NULL));
@@ -721,8 +722,10 @@ TEST(CoreUtil, ParseDelay)
     /* error: bad number */
     WEE_PARSE_DELAY(0, 0ULL, "abcd", 1LL);
 
-    /* error: bad delay */
+    /* invalid unsigned long long: outside range (0, ULLONG_MAX) */
     WEE_PARSE_DELAY(0, 0ULL, "-123", 1LL);
+    snprintf (str_delay, sizeof (str_delay), "%llu1", ULLONG_MAX);
+    LONGS_EQUAL(0, util_parse_delay (str_delay, 10, &delay));
 
     /* tests with delay == 0 */
     WEE_PARSE_DELAY(1, 0ULL, "0", 1ULL);