diff --git a/mysql-test/main/func_time.result b/mysql-test/main/func_time.result
index e5e9610da8c..8546a7bc84b 100644
--- a/mysql-test/main/func_time.result
+++ b/mysql-test/main/func_time.result
@@ -6336,3 +6336,12 @@ Warnings:
 Warning	1292	Truncated incorrect DECIMAL value: 'foo'
 Warning	1292	Truncated incorrect DECIMAL value: 'foo'
 SET time_zone=DEFAULT;
+#
+# MDEV-18402 Assertion `sec.sec() <= 59' failed in Item_func_maketime::get_date
+#
+SELECT MAKETIME('01', '01', LEAST( -100, NULL ));
+MAKETIME('01', '01', LEAST( -100, NULL ))
+NULL
+SELECT CONCAT(MAKETIME('01', '01', LEAST( -100, NULL )));
+CONCAT(MAKETIME('01', '01', LEAST( -100, NULL )))
+NULL
diff --git a/mysql-test/main/func_time.test b/mysql-test/main/func_time.test
index 212df328130..5760553e0dd 100644
--- a/mysql-test/main/func_time.test
+++ b/mysql-test/main/func_time.test
@@ -3162,3 +3162,11 @@ SELECT TIME('- 01:00:00'), TIME('- 1 01:00:00');
 SET time_zone='+00:00';
 SELECT NULLIF(FROM_UNIXTIME('foo'), '2012-12-12 21:10:14');
 SET time_zone=DEFAULT;
+
+
+--echo #
+--echo # MDEV-18402 Assertion `sec.sec() <= 59' failed in Item_func_maketime::get_date
+--echo #
+
+SELECT MAKETIME('01', '01', LEAST( -100, NULL ));
+SELECT CONCAT(MAKETIME('01', '01', LEAST( -100, NULL )));
diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index b8fd15bb5bf..2627d5413a2 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -2595,7 +2595,7 @@ bool Item_func_maketime::get_date(THD *thd, MYSQL_TIME *ltime, date_mode_t fuzzy
   longlong minute= args[1]->val_int();
   VSec9 sec(thd, args[2], "seconds", 59);
 
-  DBUG_ASSERT(sec.sec() <= 59);
+  DBUG_ASSERT(sec.is_null() || sec.sec() <= 59);
   if (args[0]->null_value || args[1]->null_value || sec.is_null() ||
        minute < 0 || minute > 59 || sec.neg() || sec.truncated())
     return (null_value= 1);