diff --git a/mysql-test/r/func_time.result b/mysql-test/r/func_time.result
index fdb4a0c5996..0e029802555 100644
--- a/mysql-test/r/func_time.result
+++ b/mysql-test/r/func_time.result
@@ -732,6 +732,25 @@ SELECT count(*) FROM t1 WHERE d>FROM_DAYS(TO_DAYS(@TMP)) AND d<=FROM_DAYS(TO_DAY
 count(*)
 3
 DROP TABLE t1;
+select last_day('2005-00-00');
+last_day('2005-00-00')
+NULL
+Warnings:
+Warning	1292	Truncated incorrect datetime value: '2005-00-00'
+select last_day('2005-00-01');
+last_day('2005-00-01')
+NULL
+Warnings:
+Warning	1292	Truncated incorrect datetime value: '2005-00-01'
+select last_day('2005-01-00');
+last_day('2005-01-00')
+NULL
+Warnings:
+Warning	1292	Truncated incorrect datetime value: '2005-01-00'
+select monthname(str_to_date(null, '%m')), monthname(str_to_date(null, '%m')),
+monthname(str_to_date(1, '%m')), monthname(str_to_date(0, '%m'));
+monthname(str_to_date(null, '%m'))	monthname(str_to_date(null, '%m'))	monthname(str_to_date(1, '%m'))	monthname(str_to_date(0, '%m'))
+NULL	NULL	January	NULL
 explain extended select timestampdiff(SQL_TSI_WEEK, '2001-02-01', '2001-05-01') as a1,
 timestampdiff(SQL_TSI_FRAC_SECOND, '2001-02-01 12:59:59.120000', '2001-05-01 12:58:58.119999') as a2;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
diff --git a/mysql-test/t/func_time.test b/mysql-test/t/func_time.test
index 4e4fb8f777a..1c7f387e354 100644
--- a/mysql-test/t/func_time.test
+++ b/mysql-test/t/func_time.test
@@ -352,6 +352,20 @@ INSERT INTO t1 VALUES (NOW());
 SELECT count(*) FROM t1 WHERE d>FROM_DAYS(TO_DAYS(@TMP)) AND d<=FROM_DAYS(TO_DAYS(@TMP)+1);
 DROP TABLE t1;
 
+#
+# Bug #10568
+#
+
+select last_day('2005-00-00');
+select last_day('2005-00-01');
+select last_day('2005-01-00');
+
+#
+# Bug #18501: monthname and NULLs
+#
+
+select monthname(str_to_date(null, '%m')), monthname(str_to_date(null, '%m')),
+       monthname(str_to_date(1, '%m')), monthname(str_to_date(0, '%m'));
 
 # End of 4.1 tests
 
diff --git a/sql/item_timefunc.cc b/sql/item_timefunc.cc
index d2fef647fb9..e997d4ae70c 100644
--- a/sql/item_timefunc.cc
+++ b/sql/item_timefunc.cc
@@ -917,9 +917,9 @@ String* Item_func_monthname::val_str(String* str)
 {
   DBUG_ASSERT(fixed == 1);
   const char *month_name;
-  uint   month=(uint) Item_func_month::val_int();
+  uint   month= (uint) val_int();
 
-  if (!month)					// This is also true for NULL
+  if (null_value || !month)
   {
     null_value=1;
     return (String*) 0;