diff --git a/BitKeeper/etc/collapsed b/BitKeeper/etc/collapsed
index 311c3813abf..226f0f1a2e2 100644
--- a/BitKeeper/etc/collapsed
+++ b/BitKeeper/etc/collapsed
@@ -15,3 +15,5 @@
 45214442pBGT9KuZEGixBH71jTzbOA
 45214a07hVsIGwvwa-WrO-jpeaSwVw
 452a92d0-31-8wSzSfZi165fcGcXPA
+454a7ef8gdvE_ddMlJyghvOAkKPNOQ
+454f8960jsVT_kMKJtZ9OCgXoba0xQ
diff --git a/mysql-test/r/func_test.result b/mysql-test/r/func_test.result
index e421fa04ecc..efae9e9f2fc 100644
--- a/mysql-test/r/func_test.result
+++ b/mysql-test/r/func_test.result
@@ -182,6 +182,80 @@ select 5.1 mod 3, 5.1 mod -3, -5.1 mod 3, -5.1 mod -3;
 select 5 mod 3, 5 mod -3, -5 mod 3, -5 mod -3;
 5 mod 3	5 mod -3	-5 mod 3	-5 mod -3
 2	2	-2	-2
+select (12%0) <=> null      as '1';
+1
+1
+select (12%0) is null       as '1';
+1
+1
+select 12%0                 as 'NULL';
+NULL
+NULL
+select 12%2                 as '0';
+0
+0
+select 12%NULL              as 'NULL';
+NULL
+NULL
+select 12 % null            as 'NULL';
+NULL
+NULL
+select null % 12            as 'NULL';
+NULL
+NULL
+select null % 0             as 'NULL';
+NULL
+NULL
+select 0 % null             as 'NULL';
+NULL
+NULL
+select null % null          as 'NULL';
+NULL
+NULL
+select (12 mod 0) <=> null  as '1';
+1
+1
+select (12 mod 0) is null   as '1';
+1
+1
+select 12 mod 0             as 'NULL';
+NULL
+NULL
+select 12 mod 2             as '0';
+0
+0
+select 12 mod null          as 'NULL';
+NULL
+NULL
+select null mod 12          as 'NULL';
+NULL
+NULL
+select null mod 0           as 'NULL';
+NULL
+NULL
+select 0 mod null           as 'NULL';
+NULL
+NULL
+select null mod null        as 'NULL';
+NULL
+NULL
+select mod(12.0, 0)         as 'NULL';
+NULL
+NULL
+select mod(12, 0.0)         as 'NULL';
+NULL
+NULL
+select mod(12, NULL)        as 'NULL';
+NULL
+NULL
+select mod(12.0, NULL)      as 'NULL';
+NULL
+NULL
+select mod(NULL, 2)         as 'NULL';
+NULL
+NULL
+select mod(NULL, 2.0)       as 'NULL';
+NULL
 create table t1 (a int, b int);
 insert into t1 values (1,2), (2,3), (3,4), (4,5);
 select * from t1 where a not between 1 and 2;
diff --git a/mysql-test/t/func_test.test b/mysql-test/t/func_test.test
index 0ea89cd0913..77bf3be5e72 100644
--- a/mysql-test/t/func_test.test
+++ b/mysql-test/t/func_test.test
@@ -108,6 +108,40 @@ select 5.1 mod 3, 5.1 mod -3, -5.1 mod 3, -5.1 mod -3;
 
 select 5 mod 3, 5 mod -3, -5 mod 3, -5 mod -3;
 
+#
+# Bug#23411: The "%" (MOD) operator is not documented; MOD-ing zero returns strange result
+# Manual: "Division by zero produces a NULL result"
+#
+select (12%0) <=> null      as '1';
+select (12%0) is null       as '1';
+select 12%0                 as 'NULL';
+select 12%2                 as '0';
+select 12%NULL              as 'NULL';
+select 12 % null            as 'NULL';
+select null % 12            as 'NULL';
+select null % 0             as 'NULL';
+select 0 % null             as 'NULL';
+select null % null          as 'NULL';
+
+select (12 mod 0) <=> null  as '1';
+select (12 mod 0) is null   as '1';
+select 12 mod 0             as 'NULL';
+select 12 mod 2             as '0';
+select 12 mod null          as 'NULL';
+select null mod 12          as 'NULL';
+select null mod 0           as 'NULL';
+select 0 mod null           as 'NULL';
+select null mod null        as 'NULL';
+
+select mod(12.0, 0)         as 'NULL';
+select mod(12, 0.0)         as 'NULL';
+select mod(12, NULL)        as 'NULL';
+select mod(12.0, NULL)      as 'NULL';
+select mod(NULL, 2)         as 'NULL';
+select mod(NULL, 2.0)       as 'NULL';
+
+
+#
 # Bug#6726: NOT BETWEEN parse failure
 #
 create table t1 (a int, b int);
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 4a069e662f9..fa17dee9605 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -105,7 +105,7 @@ Item_func::Item_func(THD *thd, Item_func *item)
 
 
 /*
-  Resolve references to table column for a function and it's argument
+  Resolve references to table column for a function and its argument
 
   SYNOPSIS:
   fix_fields()
@@ -1397,6 +1397,13 @@ void Item_func_mod::result_precision()
 }
 
 
+void Item_func_mod::fix_length_and_dec()
+{
+  Item_num_op::fix_length_and_dec();
+  maybe_null= 1;
+}
+
+
 double Item_func_neg::real_op()
 {
   double value= args[0]->val_real();