diff --git a/mysql-test/suite/json/r/json_innodb.result b/mysql-test/suite/json/r/json_innodb.result
index d00a93e304b..053544e0263 100644
--- a/mysql-test/suite/json/r/json_innodb.result
+++ b/mysql-test/suite/json/r/json_innodb.result
@@ -258,3 +258,21 @@ SUM(col_int)	col_int
 4572643328	NULL
 DROP VIEW view1;
 DROP TABLE D;
+#
+# BUG#100307: JSON field datatype changes unexpectedly
+#
+CREATE TABLE json (
+id int NOT NULL,
+j json DEFAULT NULL,
+s tinyint NOT NULL,
+PRIMARY KEY (id)
+) ENGINE=InnoDB;
+INSERT INTO json VALUES (2, '{"amount": 70.0}', 1);
+SELECT json_type(j->"$.amount") FROM json;
+json_type(j->"$.amount")
+DOUBLE
+INSERT INTO json VALUES (2, '{}', 1) ON DUPLICATE KEY UPDATE j=if(s=0, '{}', j);
+SELECT json_type(j->"$.amount") FROM json;
+json_type(j->"$.amount")
+DOUBLE
+DROP TABLE json;
diff --git a/mysql-test/suite/json/t/json_innodb.test b/mysql-test/suite/json/t/json_innodb.test
index f8388daab0c..0ec72c3dc03 100644
--- a/mysql-test/suite/json/t/json_innodb.test
+++ b/mysql-test/suite/json/t/json_innodb.test
@@ -249,3 +249,18 @@ DROP TABLE D;
 
 --source include/restore_sql_mode_after_turn_off_only_full_group_by.inc
 
+--echo #
+--echo # BUG#100307: JSON field datatype changes unexpectedly
+--echo #
+
+CREATE TABLE json (
+id int NOT NULL,
+j json DEFAULT NULL,
+s tinyint NOT NULL,
+PRIMARY KEY (id)
+) ENGINE=InnoDB;
+INSERT INTO json VALUES (2, '{"amount": 70.0}', 1);
+SELECT json_type(j->"$.amount") FROM json;
+INSERT INTO json VALUES (2, '{}', 1) ON DUPLICATE KEY UPDATE j=if(s=0, '{}', j);
+SELECT json_type(j->"$.amount") FROM json;
+DROP TABLE json;
diff --git a/sql/field.cc b/sql/field.cc
index 62663bb2c2a..57ac9063d76 100644
--- a/sql/field.cc
+++ b/sql/field.cc
@@ -9125,6 +9125,27 @@ bool Field_json::get_time(MYSQL_TIME *ltime)
   return result;
 }
 
+int Field_json::cmp_binary(const uchar *a_ptr, const uchar *b_ptr,
+                           uint32 /* max_length */)
+{
+  char *a;
+  char *b;
+  memcpy(&a, a_ptr + packlength, sizeof(a));
+  memcpy(&b, b_ptr + packlength, sizeof(b));
+  uint32 a_length= get_length(a_ptr);
+  uint32 b_length= get_length(b_ptr);
+  using namespace json_binary;
+  /*
+    The length is 0 if NULL has been inserted into a NOT NULL column
+    using INSERT IGNORE or similar. If so, interpret the value as the
+    JSON null literal.
+  */
+  Value        null_literal(Value::LITERAL_NULL);
+  Json_wrapper aw(a_length == 0 ? null_literal : parse_binary(a, a_length));
+  Json_wrapper bw(b_length == 0 ? null_literal : parse_binary(b, b_length));
+  return aw.compare(bw);
+}
+
 
 void Field_json::make_sort_key(uchar *to, size_t length)
 {
diff --git a/sql/field.h b/sql/field.h
index 0b8f06b82aa..92e624be638 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -4139,6 +4139,7 @@ public:
   Field_json *clone() const;
   uint is_equal(Create_field *new_field);
   Item_result cast_to_int_type () const { return INT_RESULT; }
+  int  cmp_binary(const uchar *a, const uchar *b, uint32 max_length= ~0L);
   void make_sort_key(uchar *to, size_t length);
 
   /**