diff --git a/mysql-test/suite/heap/btree_varchar_null.result b/mysql-test/suite/heap/btree_varchar_null.result
new file mode 100644
index 00000000000..9199cf6ef7d
--- /dev/null
+++ b/mysql-test/suite/heap/btree_varchar_null.result
@@ -0,0 +1,6 @@
+create table t1 (f1 varchar(128), f2 varchar(128), key (f2,f1) using btree) engine=memory;
+insert into t1 values (null,'not'),('one',null),('two',null),('three','');
+select * from t1 where f1 = 'one'  and f2 is null;
+f1	f2
+one	NULL
+drop table t1;
diff --git a/mysql-test/suite/heap/btree_varchar_null.test b/mysql-test/suite/heap/btree_varchar_null.test
new file mode 100644
index 00000000000..8e6625a2bfa
--- /dev/null
+++ b/mysql-test/suite/heap/btree_varchar_null.test
@@ -0,0 +1,7 @@
+#
+# MDEV-4813 Replication fails on updating a MEMORY table with an index using btree
+#
+create table t1 (f1 varchar(128), f2 varchar(128), key (f2,f1) using btree) engine=memory;
+insert into t1 values (null,'not'),('one',null),('two',null),('three','');
+select * from t1 where f1 = 'one'  and f2 is null;
+drop table t1;
diff --git a/storage/heap/hp_hash.c b/storage/heap/hp_hash.c
index 2abed55459c..2d4c0e9a031 100644
--- a/storage/heap/hp_hash.c
+++ b/storage/heap/hp_hash.c
@@ -876,8 +876,13 @@ uint hp_rb_pack_key(HP_KEYDEF *keydef, uchar *key, const uchar *old,
     if (seg->null_bit)
     {
       if (!(*key++= (char) 1 - *old++))
+      {
+	/* Add key pack length (2) to key for VARCHAR segments */
+        if (seg->type == HA_KEYTYPE_VARTEXT1)
+          old+= 2;
         continue;
       }
+    }
     if (seg->flag & HA_SWAP_KEY)
     {
       uint length= seg->length;