diff --git a/mysql-test/main/ps.result b/mysql-test/main/ps.result
index e7080a67d90..a73fd8a4948 100644
--- a/mysql-test/main/ps.result
+++ b/mysql-test/main/ps.result
@@ -5929,5 +5929,55 @@ a	b
 2	30
 DROP TABLE t1, t2;
 #
+# MDEV-33549: Incorrect handling of UPDATE in PS mode in case a table's colum declared as NOT NULL
+#
+CREATE TABLE t1 (a INT, b INT DEFAULT NULL);
+INSERT INTO t1 VALUES (20, 30);
+EXECUTE IMMEDIATE 'UPDATE t1 SET b=?' USING DEFAULT;
+SELECT * FROM t1;
+a	b
+20	NULL
+# Run twice the same update in PS mode to check
+# that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1 SET b=?';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+# Clean up
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
+# The same test for multi-table update
+CREATE TABLE t1 (a INT, b INT DEFAULT NULL);
+CREATE TABLE t2 (a INT, c INT DEFAULT NULL);
+INSERT INTO t1 VALUES (20, 30);
+INSERT INTO t2 VALUES (20, 30);
+EXECUTE IMMEDIATE 'UPDATE t1,t2 SET b=? WHERE t1.a=t2.a' USING DEFAULT;
+SELECT * FROM t1;
+a	b
+20	NULL
+# Run twice the same multi-table update in PS mode to check
+# that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1,t2 SET b=? WHERE t1.a=t2.a';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+DEALLOCATE PREPARE stmt;
+# Clean up
+DROP TABLE t1;
+# This time checks that a default value for table's column
+# represented by a function call is handled correctly on UPDATE in PS mode
+CREATE TABLE t1 (a INT, b INT DEFAULT MOD(a, 3));
+INSERT INTO t1 VALUES (20, 30);
+EXECUTE IMMEDIATE 'UPDATE t1, t2 SET b=? WHERE t1.a=t2.a' USING DEFAULT;
+SELECT * FROM t1;
+a	b
+20	2
+# Run twice the same multi-table update in PS mode to check
+# that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1, t2 SET b=? WHERE t1.a=t2.a';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+# Clean up
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1, t2;
+#
 # End of 10.4 tests
 #
diff --git a/mysql-test/main/ps.test b/mysql-test/main/ps.test
index e710050cb48..61d1513fa0b 100644
--- a/mysql-test/main/ps.test
+++ b/mysql-test/main/ps.test
@@ -5362,6 +5362,60 @@ SELECT * FROM t2;
 # Cleanup
 DROP TABLE t1, t2;
 
+--echo #
+--echo # MDEV-33549: Incorrect handling of UPDATE in PS mode in case a table's colum declared as NOT NULL
+--echo #
+
+CREATE TABLE t1 (a INT, b INT DEFAULT NULL);
+INSERT INTO t1 VALUES (20, 30);
+EXECUTE IMMEDIATE 'UPDATE t1 SET b=?' USING DEFAULT;
+SELECT * FROM t1;
+
+--echo # Run twice the same update in PS mode to check
+--echo # that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1 SET b=?';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+
+--echo # Clean up
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1;
+
+--echo # The same test for multi-table update
+CREATE TABLE t1 (a INT, b INT DEFAULT NULL);
+CREATE TABLE t2 (a INT, c INT DEFAULT NULL);
+
+INSERT INTO t1 VALUES (20, 30);
+INSERT INTO t2 VALUES (20, 30);
+
+EXECUTE IMMEDIATE 'UPDATE t1,t2 SET b=? WHERE t1.a=t2.a' USING DEFAULT;
+SELECT * FROM t1;
+--echo # Run twice the same multi-table update in PS mode to check
+--echo # that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1,t2 SET b=? WHERE t1.a=t2.a';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+DEALLOCATE PREPARE stmt;
+--echo # Clean up
+DROP TABLE t1;
+
+--echo # This time checks that a default value for table's column
+--echo # represented by a function call is handled correctly on UPDATE in PS mode
+CREATE TABLE t1 (a INT, b INT DEFAULT MOD(a, 3));
+INSERT INTO t1 VALUES (20, 30);
+EXECUTE IMMEDIATE 'UPDATE t1, t2 SET b=? WHERE t1.a=t2.a' USING DEFAULT;
+SELECT * FROM t1;
+
+--echo # Run twice the same multi-table update in PS mode to check
+--echo # that no memory relating issues taken place.
+PREPARE stmt FROM 'UPDATE t1, t2 SET b=? WHERE t1.a=t2.a';
+EXECUTE stmt USING DEFAULT;
+EXECUTE stmt USING DEFAULT;
+
+--echo # Clean up
+DEALLOCATE PREPARE stmt;
+DROP TABLE t1, t2;
+
 --echo #
 --echo # End of 10.4 tests
 --echo #
diff --git a/sql/item.cc b/sql/item.cc
index 7c8c9acca35..0e5ed30cb91 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -5131,9 +5131,19 @@ bool Item_param::assign_default(Field *field)
   }
 
   if (m_default_field->default_value)
-    m_default_field->set_default();
-
-  return field_conv(field, m_default_field);
+  {
+    return m_default_field->default_value->expr->save_in_field(field, 0);
+  }
+  else if (m_default_field->is_null())
+  {
+    field->set_null();
+    return false;
+  }
+  else
+  {
+    field->set_notnull();
+    return field_conv(field, m_default_field);
+  }
 }
 
 
diff --git a/sql/item.h b/sql/item.h
index f5c9ed2a7ab..1b696db66e9 100644
--- a/sql/item.h
+++ b/sql/item.h
@@ -3995,6 +3995,12 @@ public:
   Item_param(THD *thd, const LEX_CSTRING *name_arg,
              uint pos_in_query_arg, uint len_in_query_arg);
 
+  void cleanup() override
+  {
+    m_default_field= NULL;
+    Item::cleanup();
+  }
+
   Type type() const override
   {
     // Don't pretend to be a constant unless value for this item is set.
diff --git a/sql/mysqld.cc b/sql/mysqld.cc
index c136df0edc6..5d23a972cdc 100644
--- a/sql/mysqld.cc
+++ b/sql/mysqld.cc
@@ -2955,7 +2955,6 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
   sigset_t set;
   int sig;
   my_thread_init();				// Init new thread
-  DBUG_ENTER("signal_hand");
   signal_thread_in_use= 1;
 
   /*
@@ -3009,7 +3008,6 @@ pthread_handler_t signal_hand(void *arg __attribute__((unused)))
     {
       DBUG_PRINT("quit",("signal_handler: calling my_thread_end()"));
       my_thread_end();
-      DBUG_LEAVE;                               // Must match DBUG_ENTER()
       signal_thread_in_use= 0;
       pthread_exit(0);				// Safety
       return 0;                                 // Avoid compiler warnings