diff --git a/mysql-test/main/cset_narrowing.result b/mysql-test/main/cset_narrowing.result
index 797401c67d89b..e14d6c8cc256b 100644
--- a/mysql-test/main/cset_narrowing.result
+++ b/mysql-test/main/cset_narrowing.result
@@ -303,7 +303,7 @@ EXPLAIN
           "rows": 4,
           "cost": "COST_REPLACED",
           "filtered": 100,
-          "index_condition": "t1.mb3 = '????' or t1.mb3 = 'hello'"
+          "index_condition": "t1.mb3 = '😊' or t1.mb3 = 'hello'"
         }
       }
     ]
@@ -338,7 +338,7 @@ EXPLAIN
           "rows": 10002,
           "cost": "COST_REPLACED",
           "filtered": 100,
-          "attached_condition": "convert(t1.mb3 using utf8mb4) > '????'"
+          "attached_condition": "convert(t1.mb3 using utf8mb4) > '😊'"
         }
       }
     ]
@@ -384,7 +384,7 @@ EXPLAIN
           "rows": 3,
           "cost": "COST_REPLACED",
           "filtered": 100,
-          "index_condition": "t2.mb4 > '????'"
+          "index_condition": "t2.mb4 > '😊'"
         }
       }
     ]
diff --git a/mysql-test/main/explain_json.result b/mysql-test/main/explain_json.result
index 84cffd18424b9..81409cfbc1590 100644
--- a/mysql-test/main/explain_json.result
+++ b/mysql-test/main/explain_json.result
@@ -2305,3 +2305,64 @@ SET optimizer_trace = 'enabled=on';
 SELECT * FROM t1 WHERE a IN ( SELECT b FROM t2 INNER JOIN t1 ON (a = pk) );
 a
 DROP TABLE t1, t2;
+#
+# MDEV-16462: EXPLAIN FORMAT=JSON produces illegal json text in the attached_condition field
+#
+set names utf8mb4;
+create table t1 (
+id int(11) not null auto_increment,
+oid binary(16) not null,
+primary key (id, oid)
+);
+insert into t1 values
+(1,0x02697732663011E39AE220CF3068F21D),
+(2,0x02697732663011E39AE220CF3068F21D);
+create table t2 (
+id int(11) not null,
+oid binary(16) not null,
+primary key (id)
+);
+insert into t2 values
+(1,0x02697732663011E39AE220CF3068F21D),
+(2,0x02697732663011E39AE220CF3068F21D);
+explain format=json
+select t1.id from t1, t2 where t1.oid=t2.oid and t2.id=1;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "cost": 0.006067082,
+    "nested_loop": [
+      {
+        "table": {
+          "table_name": "t2",
+          "access_type": "const",
+          "possible_keys": ["PRIMARY"],
+          "key": "PRIMARY",
+          "key_length": "4",
+          "used_key_parts": ["id"],
+          "ref": ["const"],
+          "rows": 1,
+          "filtered": 100
+        }
+      },
+      {
+        "table": {
+          "table_name": "t1",
+          "access_type": "index",
+          "key": "PRIMARY",
+          "key_length": "20",
+          "used_key_parts": ["id", "oid"],
+          "loops": 1,
+          "rows": 2,
+          "cost": 0.006067082,
+          "filtered": 100,
+          "attached_condition": "t1.oid = 0x02697732663011E39AE220CF3068F21D",
+          "using_index": true
+        }
+      }
+    ]
+  }
+}
+drop table t1, t2;
+set names default;
diff --git a/mysql-test/main/explain_json.test b/mysql-test/main/explain_json.test
index 0d34b95070426..39d44b08544d4 100644
--- a/mysql-test/main/explain_json.test
+++ b/mysql-test/main/explain_json.test
@@ -500,3 +500,33 @@ INSERT INTO t2 VALUES
 SET optimizer_trace = 'enabled=on';
 SELECT * FROM t1 WHERE a IN ( SELECT b FROM t2 INNER JOIN t1 ON (a = pk) );
 DROP TABLE t1, t2;
+
+--echo #
+--echo # MDEV-16462: EXPLAIN FORMAT=JSON produces illegal json text in the attached_condition field
+--echo #
+set names utf8mb4;
+create table t1 (
+  id int(11) not null auto_increment,
+  oid binary(16) not null,
+  primary key (id, oid)
+);
+
+insert into t1 values
+(1,0x02697732663011E39AE220CF3068F21D),
+(2,0x02697732663011E39AE220CF3068F21D);
+
+create table t2 (
+  id int(11) not null,
+  oid binary(16) not null,
+  primary key (id)
+);
+
+insert into t2 values
+(1,0x02697732663011E39AE220CF3068F21D),
+(2,0x02697732663011E39AE220CF3068F21D);
+
+explain format=json
+select t1.id from t1, t2 where t1.oid=t2.oid and t2.id=1;
+
+drop table t1, t2;
+set names default;
diff --git a/sql/item.cc b/sql/item.cc
index 3bdd7f82da327..e9bf4c61af0c8 100644
--- a/sql/item.cc
+++ b/sql/item.cc
@@ -555,6 +555,16 @@ void Item::print_value(String *str)
   {
     switch (cmp_type()) {
     case STRING_RESULT:
+      if (ptr->charset() == &my_charset_bin && ptr->length())
+      {
+        StringBuffer<64> escaped_val;
+        escaped_val.set_hex(ptr->ptr(), ptr->length());
+        str->append(STRING_WITH_LEN("0x"));
+        str->append(escaped_val);
+      }
+      else
+        append_unescaped(str, ptr->ptr(), ptr->length());
+      break;
     case TIME_RESULT:
       append_unescaped(str, ptr->ptr(), ptr->length());
       break;
diff --git a/sql/sql_explain.cc b/sql/sql_explain.cc
index 77aab40092f65..288dd0637c786 100644
--- a/sql/sql_explain.cc
+++ b/sql/sql_explain.cc
@@ -211,15 +211,15 @@ int Explain_query::send_explain(THD *thd, bool extended)
     if (extended)
     {
       char buff[1024];
-      String str(buff,(uint32) sizeof(buff), system_charset_info);
-                 str.length(0);
-     /*
-       The warnings system requires input in utf8, @see
-        mysqld_show_warnings().
-     */
-     lex->unit.print(&str, QT_EXPLAIN_EXTENDED);
-                     push_warning(thd, Sql_condition::WARN_LEVEL_NOTE,
-                     ER_YES, str.c_ptr_safe());
+      String str(buff, (uint32) sizeof(buff), &my_charset_utf8mb4_bin);
+      str.length(0);
+      /*
+        The warnings system requires input in utf8, @see
+         mysqld_show_warnings().
+      */
+      lex->unit.print(&str, QT_EXPLAIN_EXTENDED);
+      push_warning(thd, Sql_condition::WARN_LEVEL_NOTE, ER_YES,
+                   str.c_ptr_safe());
     }
   }
   if (res)
@@ -330,7 +330,7 @@ bool Explain_query::print_query_blocks_json(Json_writer *writer, const bool is_a
 void Explain_query::send_explain_json_to_output(Json_writer *writer, 
                                                 select_result_sink *output)
 {
-  CHARSET_INFO *cs= system_charset_info;
+  CHARSET_INFO *cs= &my_charset_utf8mb4_bin;
   List<Item> item_list;
   const String *buf= writer->output.get_string();
   THD *thd= output->thd;
@@ -1287,7 +1287,7 @@ void Explain_aggr_filesort::print_json_members(Json_writer *writer,
                                                bool is_analyze)
 {
   char item_buf[256];
-  String str(item_buf, sizeof(item_buf), &my_charset_bin);
+  String str(item_buf, sizeof(item_buf), &my_charset_utf8mb4_bin);
   str.length(0);
   
   List_iterator_fast<Item> it(sort_items);
@@ -1389,7 +1389,7 @@ void Explain_table_access::push_extra(enum explain_extra_tag extra_tag)
 
 void Explain_table_access::fill_key_str(String *key_str, bool is_json) const
 {
-  CHARSET_INFO *cs= system_charset_info;
+  CHARSET_INFO *cs= &my_charset_utf8mb4_bin;
   bool is_hj= (type == JT_HASH || type == JT_HASH_NEXT || 
                type == JT_HASH_RANGE || type == JT_HASH_INDEX_MERGE);
   LEX_CSTRING hash_key_prefix= { STRING_WITH_LEN("#hash#") };
@@ -1775,7 +1775,7 @@ static void write_item(Json_writer *writer, Item *item)
 {
   THD *thd= current_thd;
   char item_buf[256];
-  String str(item_buf, sizeof(item_buf), &my_charset_bin);
+  String str(item_buf, sizeof(item_buf), &my_charset_utf8mb4_bin);
   str.length(0);
 
   ulonglong save_option_bits= thd->variables.option_bits;
@@ -1784,7 +1784,7 @@ static void write_item(Json_writer *writer, Item *item)
   item->print(&str, QT_EXPLAIN);
 
   thd->variables.option_bits= save_option_bits;
-  writer->add_str(str.c_ptr_safe());
+  writer->add_str(str.c_ptr_safe(), str.length());
 }
 
 static void append_item_to_str(String *out, Item *item)
@@ -2739,10 +2739,10 @@ int Explain_update::print_explain(Explain_query *query,
   else if (key.get_key_name())
   {
     const char *name= key.get_key_name();
-    key_buf.set(name, strlen(name), &my_charset_bin);
+    key_buf.set(name, strlen(name), &my_charset_utf8mb4_bin);
     char buf[64];
     size_t length= longlong10_to_str(key.get_key_len(), buf, 10) - buf;
-    key_len_buf.copy(buf, length, &my_charset_bin);
+    key_len_buf.copy(buf, length, &my_charset_utf8mb4_bin);
   }
 
   if (using_where)