diff --git a/mysql-test/r/join_cache.result b/mysql-test/r/join_cache.result
index bbe326d7b19..9f054984416 100644
--- a/mysql-test/r/join_cache.result
+++ b/mysql-test/r/join_cache.result
@@ -6122,4 +6122,50 @@ f1	f3	f3	f2	f4
 SET SESSION join_cache_level = DEFAULT;
 SET SESSION optimizer_switch = DEFAULT;
 DROP TABLE t1,t2;
+#
+# Bug #694443: hash join using IS NULL the an equi-join condition
+#
+CREATE TABLE t1 (a int PRIMARY KEY);
+INSERT INTO t1 VALUES
+(7), (4), (9), (1), (3), (8), (2);
+CREATE TABLE t2 (a int, b int, INDEX idx (a));
+INSERT INTO t2 VALUES
+(NULL,10), (4,80), (7,70), (6,11), (7,90), (NULL,40),
+(4,77), (4,50), (NULL,41), (7,99), (7,88), (8,12),
+(1,21), (4,90), (7,91), (8,22), (6,92), (NULL,42),
+(2,78), (2,51), (1,43), (5,97), (5,89);
+SET SESSION join_cache_level = 1;
+EXPLAIN 
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	PRIMARY	PRIMARY	4	NULL	3	Using where; Using index
+1	SIMPLE	t2	ref	idx	idx	5	const	4	Using index condition
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+a	a	b
+1	NULL	10
+1	NULL	40
+1	NULL	41
+1	NULL	42
+2	NULL	10
+2	NULL	40
+2	NULL	41
+2	NULL	42
+SET SESSION join_cache_level = 4;
+EXPLAIN 
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	range	PRIMARY	PRIMARY	4	NULL	3	Using where; Using index
+1	SIMPLE	t2	ref	idx	idx	5	const	4	Using where; Using join buffer (flat, BNLH join)
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+a	a	b
+1	NULL	10
+2	NULL	10
+1	NULL	40
+2	NULL	40
+1	NULL	41
+2	NULL	41
+1	NULL	42
+2	NULL	42
+SET SESSION join_cache_level = DEFAULT;
+DROP TABLE t1,t2;
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/mysql-test/t/join_cache.test b/mysql-test/t/join_cache.test
index e538422475e..b2b3413da9b 100644
--- a/mysql-test/t/join_cache.test
+++ b/mysql-test/t/join_cache.test
@@ -2759,5 +2759,36 @@ SET SESSION optimizer_switch = DEFAULT;
 
 DROP TABLE t1,t2;
 
+--echo #
+--echo # Bug #694443: hash join using IS NULL the an equi-join condition
+--echo #
+
+CREATE TABLE t1 (a int PRIMARY KEY);
+INSERT INTO t1 VALUES
+  (7), (4), (9), (1), (3), (8), (2);
+
+CREATE TABLE t2 (a int, b int, INDEX idx (a));
+INSERT INTO t2 VALUES
+  (NULL,10), (4,80), (7,70), (6,11), (7,90), (NULL,40),
+  (4,77), (4,50), (NULL,41), (7,99), (7,88), (8,12),
+  (1,21), (4,90), (7,91), (8,22), (6,92), (NULL,42),
+  (2,78), (2,51), (1,43), (5,97), (5,89);
+
+SET SESSION join_cache_level = 1;
+EXPLAIN 
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+
+SET SESSION join_cache_level = 4;
+EXPLAIN 
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+SELECT * FROM t1,t2 WHERE t1.a < 3 and t2.a IS NULL;
+
+
+SET SESSION join_cache_level = DEFAULT;
+
+DROP TABLE t1,t2;
+  
+
 # this must be the last command in the file
 set @@optimizer_switch=@save_optimizer_switch;
diff --git a/sql/key.cc b/sql/key.cc
index 0de1d1fd642..780cc6733c1 100644
--- a/sql/key.cc
+++ b/sql/key.cc
@@ -103,10 +103,11 @@ int find_ref_key(KEY *key, uint key_count, uchar *record, Field *field,
   @param from_record full record to be copied from
   @param key_info    descriptor of the index
   @param key_length  specifies length of all keyparts that will be copied
+  @param with_zerofill  skipped bytes in the key buffer to be filled with 0
 */
 
 void key_copy(uchar *to_key, uchar *from_record, KEY *key_info,
-              uint key_length)
+              uint key_length, bool with_zerofill)
 {
   uint length;
   KEY_PART_INFO *key_part;
@@ -129,6 +130,8 @@ void key_copy(uchar *to_key, uchar *from_record, KEY *key_info,
           The -1 below is to subtract the null byte which is already handled
         */
         length= min(key_length, (uint) key_part->store_length-1);
+        if (with_zerofill)
+          bzero((char*) to_key, length);
         continue;
       }
     }
@@ -137,7 +140,9 @@ void key_copy(uchar *to_key, uchar *from_record, KEY *key_info,
     {
       key_length-= HA_KEY_BLOB_LENGTH;
       length= min(key_length, key_part->length);
-      key_part->field->get_key_image(to_key, length, Field::itRAW);
+      uint bytes= key_part->field->get_key_image(to_key, length, Field::itRAW);
+      if (with_zerofill && bytes < length)
+        bzero((char*) to_key + bytes, length - bytes);
       to_key+= HA_KEY_BLOB_LENGTH;
     }
     else
diff --git a/sql/mysql_priv.h b/sql/mysql_priv.h
index ca5ccc699cd..0c929c535c5 100644
--- a/sql/mysql_priv.h
+++ b/sql/mysql_priv.h
@@ -1876,7 +1876,8 @@ void mysql_print_status();
 /* key.cc */
 int find_ref_key(KEY *key, uint key_count, uchar *record, Field *field,
                  uint *key_length, uint *keypart);
-void key_copy(uchar *to_key, uchar *from_record, KEY *key_info, uint key_length);
+void key_copy(uchar *to_key, uchar *from_record, KEY *key_info, uint key_length,
+              bool with_zerofill= FALSE);
 void key_restore(uchar *to_record, uchar *from_key, KEY *key_info,
                  uint key_length);
 bool key_cmp_if_same(TABLE *form,const uchar *key,uint index,uint key_length);
diff --git a/sql/sql_join_cache.cc b/sql/sql_join_cache.cc
index 01635c56585..6c94ccede47 100644
--- a/sql/sql_join_cache.cc
+++ b/sql/sql_join_cache.cc
@@ -3429,7 +3429,7 @@ uchar *JOIN_CACHE_BNLH::get_matching_chain_by_join_key()
   TABLE_REF *ref= &join_tab->ref;
   KEY *keyinfo= table->key_info+ref->key;
   /* Build the join key value out of the record in the record buffer */
-  key_copy(key_buff, table->record[0], keyinfo, key_length);
+  key_copy(key_buff, table->record[0], keyinfo, key_length, TRUE);
   /* Look for this key in the join buffer */
   if (!key_search(key_buff, key_length, &key_ref_ptr))
     return 0;