diff --git a/BitKeeper/etc/collapsed b/BitKeeper/etc/collapsed
index a4f24702b58..0eb8a32482d 100644
--- a/BitKeeper/etc/collapsed
+++ b/BitKeeper/etc/collapsed
@@ -5,3 +5,5 @@
 4513d8e4Af4dQWuk13sArwofRgFDQw
 4519a6c5BVUxEHTf5iJnjZkixMBs8g
 451ab499rgdjXyOnUDqHu-wBDoS-OQ
+45214442pBGT9KuZEGixBH71jTzbOA
+45214a07hVsIGwvwa-WrO-jpeaSwVw
diff --git a/mysql-test/r/ps_11bugs.result b/mysql-test/r/ps_11bugs.result
index c849c25d646..ebe161f46b3 100644
--- a/mysql-test/r/ps_11bugs.result
+++ b/mysql-test/r/ps_11bugs.result
@@ -130,3 +130,36 @@ prepare st_18492 from 'select * from t1 where 3 in (select (1+1) union select 1)
 execute st_18492;
 a
 drop table t1;
+create table t1 (a int, b varchar(4));
+create table t2 (a int, b varchar(4), primary key(a));
+prepare stmt1 from 'insert into t1 (a, b) values (?, ?)';
+prepare stmt2 from 'insert into t2 (a, b) values (?, ?)';
+set @intarg= 11;
+set @varchararg= '2222';
+execute stmt1 using @intarg, @varchararg;
+execute stmt2 using @intarg, @varchararg;
+set @intarg= 12;
+execute stmt1 using @intarg, @UNDEFINED;
+execute stmt2 using @intarg, @UNDEFINED;
+set @intarg= 13;
+execute stmt1 using @UNDEFINED, @varchararg;
+execute stmt2 using @UNDEFINED, @varchararg;
+ERROR 23000: Column 'a' cannot be null
+set @intarg= 14;
+set @nullarg= Null;
+execute stmt1 using @UNDEFINED, @nullarg;
+execute stmt2 using @nullarg, @varchararg;
+ERROR 23000: Column 'a' cannot be null
+select * from t1;
+a	b
+11	2222
+12	NULL
+NULL	2222
+NULL	NULL
+select * from t2;
+a	b
+11	2222
+12	NULL
+drop table t1;
+drop table t2;
+End of 5.0 tests.
diff --git a/mysql-test/t/ps_11bugs.test b/mysql-test/t/ps_11bugs.test
index ff1c87f3bd8..515bcc03c1a 100644
--- a/mysql-test/t/ps_11bugs.test
+++ b/mysql-test/t/ps_11bugs.test
@@ -144,3 +144,37 @@ prepare st_18492 from 'select * from t1 where 3 in (select (1+1) union select 1)
 execute st_18492;
 
 drop table t1;
+
+#
+# Bug#19356: Assertion failure with undefined @uservar in prepared statement execution
+# 
+create table t1 (a int, b varchar(4));
+create table t2 (a int, b varchar(4), primary key(a));
+
+prepare stmt1 from 'insert into t1 (a, b) values (?, ?)';
+prepare stmt2 from 'insert into t2 (a, b) values (?, ?)';
+
+set @intarg= 11;
+set @varchararg= '2222';
+execute stmt1 using @intarg, @varchararg;
+execute stmt2 using @intarg, @varchararg;
+set @intarg= 12;
+execute stmt1 using @intarg, @UNDEFINED;
+execute stmt2 using @intarg, @UNDEFINED;
+set @intarg= 13;
+execute stmt1 using @UNDEFINED, @varchararg;
+--error 1048
+execute stmt2 using @UNDEFINED, @varchararg;
+set @intarg= 14;
+set @nullarg= Null;
+execute stmt1 using @UNDEFINED, @nullarg;
+--error 1048
+execute stmt2 using @nullarg, @varchararg;
+
+select * from t1;
+select * from t2;
+
+drop table t1;
+drop table t2;
+
+--echo End of 5.0 tests.
diff --git a/sql/sql_prepare.cc b/sql/sql_prepare.cc
index 63a129918d0..fa33cafdab1 100644
--- a/sql/sql_prepare.cc
+++ b/sql/sql_prepare.cc
@@ -2287,6 +2287,14 @@ void mysql_stmt_execute(THD *thd, char *packet_arg, uint packet_length)
 #endif
   if (!(specialflag & SPECIAL_NO_PRIOR))
     my_pthread_setprio(pthread_self(),QUERY_PRIOR);
+
+  /*
+    If the free_list is not empty, we'll wrongly free some externally
+    allocated items when cleaning up after validation of the prepared
+    statement.
+  */
+  DBUG_ASSERT(thd->free_list == NULL);
+
   error= stmt->execute(&expanded_query,
                        test(flags & (ulong) CURSOR_TYPE_READ_ONLY));
   if (!(specialflag & SPECIAL_NO_PRIOR))
@@ -2349,6 +2357,13 @@ void mysql_sql_stmt_execute(THD *thd)
 
   DBUG_PRINT("info",("stmt: %p", stmt));
 
+  /*
+    If the free_list is not empty, we'll wrongly free some externally
+    allocated items when cleaning up after validation of the prepared
+    statement.
+  */
+  DBUG_ASSERT(thd->free_list == NULL);
+
   if (stmt->set_params_from_vars(stmt, lex->prepared_stmt_params,
                                  &expanded_query))
     goto set_params_data_err;
@@ -2827,12 +2842,12 @@ bool Prepared_statement::prepare(const char *packet, uint packet_len)
     external changes when cleaning up after validation.
   */
   DBUG_ASSERT(thd->change_list.is_empty());
-  /*
-    If the free_list is not empty, we'll wrongly free some externally
-    allocated items when cleaning up after validation of the prepared
-    statement.
+
+  /* 
+   The only case where we should have items in the thd->free_list is
+   after stmt->set_params_from_vars(), which may in some cases create
+   Item_null objects.
   */
-  DBUG_ASSERT(thd->free_list == NULL);
 
   if (error == 0)
     error= check_prepared_statement(this, name.str != 0);
@@ -2930,7 +2945,13 @@ bool Prepared_statement::execute(String *expanded_query, bool open_cursor)
     allocated items when cleaning up after execution of this statement.
   */
   DBUG_ASSERT(thd->change_list.is_empty());
-  DBUG_ASSERT(thd->free_list == NULL);
+
+  /* 
+   The only case where we should have items in the thd->free_list is
+   after stmt->set_params_from_vars(), which may in some cases create
+   Item_null objects.
+  */
+
   thd->set_n_backup_statement(this, &stmt_backup);
   if (expanded_query->length() &&
       alloc_query(thd, (char*) expanded_query->ptr(),