diff --git a/mysql-test/r/func_str.result b/mysql-test/r/func_str.result
index 3d9c9bc15d9..06cfa233f73 100644
--- a/mysql-test/r/func_str.result
+++ b/mysql-test/r/func_str.result
@@ -2980,6 +2980,49 @@ select md5(_filename "a"), sha(_filename "a");
 md5(_filename "a")	sha(_filename "a")
 0cc175b9c0f1b6a831c399e269772661	86f7e437faa5a7fce15d1ddcb9eaeaea377667b8
 #
+# MDEV-18881 Assertion `0' failed in make_sortkey upon SELECT with GROUP BY after LOAD DATA
+#
+CREATE TABLE t1 (a BIT(22), b CHAR(8) NOT NULL, c CHAR(8));
+INSERT INTO t1 VALUES (0xA4B,'foo','qux');
+INSERT INTO t1 VALUES (0x8F5,'bar','foobar');
+INSERT INTO t1 VALUES (0x0, '', NULL);
+INSERT INTO t1 VALUES (0x4B, 'foo','qux');
+INSERT INTO t1 VALUES (0x8F5, 'bar', 'foobar');
+SET SESSION SQL_MODE= '';
+SELECT GROUP_CONCAT(c) AS f FROM t1 GROUP BY LPAD('foo', 20, b);
+f
+NULL
+foobar,foobar
+qux,qux
+DROP TABLE t1;
+SET SESSION SQL_MODE=DEFAULT;
+CREATE TABLE t1 AS SELECT
+LPAD('a',10,' '),
+RPAD('a',10,' '),
+LPAD('a',10,'  '),
+RPAD('a',10,'  '),
+LPAD('a',10,NULL),
+RPAD('a',10,NULL),
+LPAD('a',10,''),
+RPAD('a',10,''),
+LPAD('a',10,RAND()),
+RPAD('a',10,RAND());
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `LPAD('a',10,' ')` varchar(10) NOT NULL,
+  `RPAD('a',10,' ')` varchar(10) NOT NULL,
+  `LPAD('a',10,'  ')` varchar(10) NOT NULL,
+  `RPAD('a',10,'  ')` varchar(10) NOT NULL,
+  `LPAD('a',10,NULL)` varchar(10) DEFAULT NULL,
+  `RPAD('a',10,NULL)` varchar(10) DEFAULT NULL,
+  `LPAD('a',10,'')` varchar(10) DEFAULT NULL,
+  `RPAD('a',10,'')` varchar(10) DEFAULT NULL,
+  `LPAD('a',10,RAND())` varchar(10) DEFAULT NULL,
+  `RPAD('a',10,RAND())` varchar(10) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1;
+#
 # End of 5.5 tests
 #
 #
diff --git a/mysql-test/t/func_str.test b/mysql-test/t/func_str.test
index 46b4dc2e3f0..de954d2f60b 100644
--- a/mysql-test/t/func_str.test
+++ b/mysql-test/t/func_str.test
@@ -1610,6 +1610,36 @@ drop table t1,t2;
 #
 select md5(_filename "a"), sha(_filename "a");
 
+--echo #
+--echo # MDEV-18881 Assertion `0' failed in make_sortkey upon SELECT with GROUP BY after LOAD DATA
+--echo #
+
+CREATE TABLE t1 (a BIT(22), b CHAR(8) NOT NULL, c CHAR(8));
+INSERT INTO t1 VALUES (0xA4B,'foo','qux');
+INSERT INTO t1 VALUES (0x8F5,'bar','foobar');
+INSERT INTO t1 VALUES (0x0, '', NULL);
+INSERT INTO t1 VALUES (0x4B, 'foo','qux');
+INSERT INTO t1 VALUES (0x8F5, 'bar', 'foobar');
+SET SESSION SQL_MODE= '';
+SELECT GROUP_CONCAT(c) AS f FROM t1 GROUP BY LPAD('foo', 20, b);
+DROP TABLE t1;
+SET SESSION SQL_MODE=DEFAULT;
+
+CREATE TABLE t1 AS SELECT
+  LPAD('a',10,' '),
+  RPAD('a',10,' '),
+  LPAD('a',10,'  '),
+  RPAD('a',10,'  '),
+  LPAD('a',10,NULL),
+  RPAD('a',10,NULL),
+  LPAD('a',10,''),
+  RPAD('a',10,''),
+  LPAD('a',10,RAND()),
+  RPAD('a',10,RAND());
+SHOW CREATE TABLE t1;
+DROP TABLE t1;
+
+
 --echo #
 --echo # End of 5.5 tests
 --echo #
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index 73080d9f7fe..de13999bab8 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -3066,8 +3066,12 @@ err:
 }
 
 
-void Item_func_rpad::fix_length_and_dec()
+void Item_func_pad::fix_length_and_dec()
 {
+  String *str;
+  if (!args[2]->basic_const_item() || !(str= args[2]->val_str(&pad_str)) || !str->length())
+    maybe_null= true;
+
   // Handle character set for args[0] and args[2].
   if (agg_arg_charsets_for_string_result(collation, &args[0], 2, 2))
     return;
@@ -3101,7 +3105,7 @@ String *Item_func_rpad::val_str(String *str)
   longlong count= args[1]->val_int();
   longlong byte_count;
   String *res= args[0]->val_str(str);
-  String *rpad= args[2]->val_str(&rpad_str);
+  String *rpad= args[2]->val_str(&pad_str);
 
   if (!res || args[1]->null_value || !rpad || 
       ((count < 0) && !args[1]->unsigned_flag))
@@ -3174,32 +3178,6 @@ String *Item_func_rpad::val_str(String *str)
 }
 
 
-void Item_func_lpad::fix_length_and_dec()
-{
-  // Handle character set for args[0] and args[2].
-  if (agg_arg_charsets_for_string_result(collation, &args[0], 2, 2))
-    return;
-  
-  if (args[1]->const_item())
-  {
-    ulonglong char_length= (ulonglong) args[1]->val_int();
-    DBUG_ASSERT(collation.collation->mbmaxlen > 0);
-    /* Assumes that the maximum length of a String is < INT_MAX32. */
-    /* Set here so that rest of code sees out-of-bound value as such. */
-    if (args[1]->null_value)
-      char_length= 0;
-    else if (char_length > INT_MAX32)
-      char_length= INT_MAX32;
-    fix_char_length_ulonglong(char_length);
-  }
-  else
-  {
-    max_length= MAX_BLOB_WIDTH;
-    maybe_null= 1;
-  }
-}
-
-
 String *Item_func_lpad::val_str(String *str)
 {
   DBUG_ASSERT(fixed == 1);
@@ -3208,7 +3186,7 @@ String *Item_func_lpad::val_str(String *str)
   longlong count= args[1]->val_int();
   longlong byte_count;
   String *res= args[0]->val_str(&tmp_value);
-  String *pad= args[2]->val_str(&lpad_str);
+  String *pad= args[2]->val_str(&pad_str);
 
   if (!res || args[1]->null_value || !pad ||  
       ((count < 0) && !args[1]->unsigned_flag))
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index 49faed2fec1..ace246bc271 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -823,26 +823,33 @@ public:
 };
 
 
-class Item_func_rpad :public Item_str_func
+class Item_func_pad: public Item_str_func
+{
+protected:
+  String tmp_value, pad_str;
+public:
+  Item_func_pad(THD *thd, Item *arg1, Item *arg2, Item *arg3):
+    Item_str_func(thd, arg1, arg2, arg3) {}
+  void fix_length_and_dec();
+};
+
+
+class Item_func_rpad :public Item_func_pad
 {
-  String tmp_value, rpad_str;
 public:
   Item_func_rpad(THD *thd, Item *arg1, Item *arg2, Item *arg3):
-    Item_str_func(thd, arg1, arg2, arg3) {}
+    Item_func_pad(thd, arg1, arg2, arg3) {}
   String *val_str(String *);
-  void fix_length_and_dec();
   const char *func_name() const { return "rpad"; }
 };
 
 
-class Item_func_lpad :public Item_str_func
+class Item_func_lpad :public Item_func_pad
 {
-  String tmp_value, lpad_str;
 public:
   Item_func_lpad(THD *thd, Item *arg1, Item *arg2, Item *arg3):
-    Item_str_func(thd, arg1, arg2, arg3) {}
+    Item_func_pad(thd, arg1, arg2, arg3) {}
   String *val_str(String *);
-  void fix_length_and_dec();
   const char *func_name() const { return "lpad"; }
 };