diff --git a/lib/fluent/config/types.rb b/lib/fluent/config/types.rb
index 66ef37ad39..98e7d0d9d8 100644
--- a/lib/fluent/config/types.rb
+++ b/lib/fluent/config/types.rb
@@ -20,6 +20,10 @@
 
 module Fluent
   module Config
+    def self.reformatted_value(type, val, opts = {}, name = nil)
+      REFORMAT_VALUE.call(type, val, opts, name)
+    end
+
     def self.size_value(str, opts = {}, name = nil)
       return nil if str.nil?
 
@@ -104,6 +108,16 @@ def self.string_value(val, opts = {}, name = nil)
       Config.string_value(val, opts, name)
     }
 
+    def self.symbol_value(val, opts = {}, name = nil)
+      return nil if val.nil? || val.empty?
+
+      val.delete_prefix(":").to_sym
+    end
+
+    SYMBOL_TYPE = Proc.new { |val, opts = {}, name = nil|
+      Config.symbol_value(val, opts, name)
+    }
+
     def self.enum_value(val, opts = {}, name = nil)
       return nil if val.nil?
 
@@ -176,6 +190,7 @@ def self.enum_value(val, opts = {}, name = nil)
         when :bool then Config.bool_value(value, opts, name)
         when :time then Config.time_value(value, opts, name)
         when :regexp then Config.regexp_value(value, opts, name)
+        when :symbol then Config.symbol_value(value, opts, name)
         else
           raise "unknown type in REFORMAT: #{type}"
         end
diff --git a/lib/fluent/env.rb b/lib/fluent/env.rb
index 2b0bf5c8d7..5ddf505bc2 100644
--- a/lib/fluent/env.rb
+++ b/lib/fluent/env.rb
@@ -15,13 +15,14 @@
 #
 
 require 'serverengine/utils'
+require 'fluent/oj_options'
 
 module Fluent
   DEFAULT_CONFIG_PATH = ENV['FLUENT_CONF'] || '/etc/fluent/fluent.conf'
   DEFAULT_PLUGIN_DIR = ENV['FLUENT_PLUGIN'] || '/etc/fluent/plugin'
   DEFAULT_SOCKET_PATH = ENV['FLUENT_SOCKET'] || '/var/run/fluent/fluent.sock'
   DEFAULT_BACKUP_DIR = ENV['FLUENT_BACKUP_DIR'] || '/tmp/fluent'
-  DEFAULT_OJ_OPTIONS = {bigdecimal_load: :float, mode: :compat, use_to_json: true}
+  DEFAULT_OJ_OPTIONS = Fluent::OjOptions.load_env
   DEFAULT_DIR_PERMISSION = 0755
   DEFAULT_FILE_PERMISSION = 0644
 
diff --git a/lib/fluent/oj_options.rb b/lib/fluent/oj_options.rb
new file mode 100644
index 0000000000..f1c274c119
--- /dev/null
+++ b/lib/fluent/oj_options.rb
@@ -0,0 +1,62 @@
+require 'fluent/config/types'
+
+module Fluent
+  class OjOptions
+    OPTIONS = {
+      'bigdecimal_load': :symbol,
+      'max_nesting': :integer,
+      'mode': :symbol,
+      'use_to_json': :bool
+    }
+
+    ALLOWED_VALUES = {
+      'bigdecimal_load': %i[bigdecimal float auto],
+      'mode': %i[strict null compat json rails object custom]
+    }
+
+    DEFAULTS = {
+      'bigdecimal_load': :float,
+      'mode': :compat,
+      'use_to_json': true
+    }
+
+    @@available = false
+
+    def self.available?
+      @@available
+    end
+
+    def self.load_env
+      options = self.get_options
+      begin
+        require 'oj'
+        Oj.default_options = options
+        @@available = true
+      rescue LoadError
+        @@available = false
+      end
+      options
+    end
+
+    private
+
+    def self.get_options
+      options = {}
+      DEFAULTS.each { |key, value| options[key] = value }
+
+      OPTIONS.each do |key, type|
+        env_value = ENV["FLUENT_OJ_OPTION_#{key.upcase}"]
+        next if env_value.nil?
+
+        cast_value = Fluent::Config.reformatted_value(OPTIONS[key], env_value, { strict: true })
+        next if cast_value.nil?
+
+        next if ALLOWED_VALUES[key] && !ALLOWED_VALUES[key].include?(cast_value)
+
+        options[key.to_sym] = cast_value
+      end
+
+      options
+    end
+  end
+end
diff --git a/lib/fluent/plugin/formatter_json.rb b/lib/fluent/plugin/formatter_json.rb
index 180d23eeca..8d850f28fb 100644
--- a/lib/fluent/plugin/formatter_json.rb
+++ b/lib/fluent/plugin/formatter_json.rb
@@ -15,7 +15,7 @@
 #
 
 require 'fluent/plugin/formatter'
-require 'fluent/env'
+require 'fluent/oj_options'
 
 module Fluent
   module Plugin
@@ -30,12 +30,14 @@ class JSONFormatter < Formatter
       def configure(conf)
         super
 
-        begin
-          raise LoadError unless @json_parser == 'oj'
-          require 'oj'
-          Oj.default_options = Fluent::DEFAULT_OJ_OPTIONS
-          @dump_proc = Oj.method(:dump)
-        rescue LoadError
+        if @json_parser == 'oj'
+          if Fluent::OjOptions.available?
+            @dump_proc = Oj.method(:dump)
+          else
+            log.info "Oj isn't installed, fallback to Yajl as json parser"
+            @dump_proc = Yajl.method(:dump)
+          end
+        else
           @dump_proc = Yajl.method(:dump)
         end
 
diff --git a/lib/fluent/plugin/parser_json.rb b/lib/fluent/plugin/parser_json.rb
index ea6fa657a3..840f6a963c 100644
--- a/lib/fluent/plugin/parser_json.rb
+++ b/lib/fluent/plugin/parser_json.rb
@@ -15,8 +15,8 @@
 #
 
 require 'fluent/plugin/parser'
-require 'fluent/env'
 require 'fluent/time'
+require 'fluent/oj_options'
 
 require 'yajl'
 require 'json'
@@ -50,8 +50,7 @@ def configure(conf)
       def configure_json_parser(name)
         case name
         when :oj
-          require 'oj'
-          Oj.default_options = Fluent::DEFAULT_OJ_OPTIONS
+          raise LoadError unless Fluent::OjOptions.available?
           [Oj.method(:load), Oj::ParseError]
         when :json then [JSON.method(:load), JSON::ParserError]
         when :yajl then [Yajl.method(:load), Yajl::ParseError]
diff --git a/test/config/test_types.rb b/test/config/test_types.rb
index 5217204030..9d7b9825a9 100644
--- a/test/config/test_types.rb
+++ b/test/config/test_types.rb
@@ -180,6 +180,13 @@ class TestConfigTypes < ::Test::Unit::TestCase
       assert_equal Encoding::UTF_8, actual.encoding
     end
 
+    data('starts_with_semicolon' => [:conor, ':conor'],
+         'simple_string' => [:conor, 'conor'],
+         'empty_string' => [nil, ''])
+    test 'symbol' do |(expected, val)|
+      assert_equal Config::SYMBOL_TYPE.call(val, {}), expected
+    end
+
     data("val" => [:val, 'val'],
          "v" => [:v, 'v'],
          "value" => [:value, 'value'])
diff --git a/test/test_event_time.rb b/test/test_event_time.rb
index 581a276e57..6ce82f5cc8 100644
--- a/test/test_event_time.rb
+++ b/test/test_event_time.rb
@@ -64,8 +64,8 @@ class EventTimeTest < Test::Unit::TestCase
 
   test 'Oj.dump' do
     time = Fluent::EventTime.new(100)
-    require 'fluent/env'
-    Oj.default_options = Fluent::DEFAULT_OJ_OPTIONS
+    require 'fluent/oj_options'
+    Fluent::OjOptions.load_env
     assert_equal('{"time":100}', Oj.dump({'time' => time}))
     assert_equal('["tag",100,{"key":"value"}]', Oj.dump(["tag", time, {"key" => "value"}], mode: :compat))
   end
diff --git a/test/test_oj_options.rb b/test/test_oj_options.rb
new file mode 100644
index 0000000000..cf91612d0c
--- /dev/null
+++ b/test/test_oj_options.rb
@@ -0,0 +1,55 @@
+require_relative 'helper'
+require 'fluent/test'
+require 'fluent/oj_options'
+
+class OjOptionsTest < ::Test::Unit::TestCase
+  begin
+    require 'oj'
+    @@oj_is_avaibale = true
+  rescue LoadError
+    @@oj_is_avaibale = false
+  end
+
+  setup do
+    @orig_env = {}
+    ENV.each do |key, value|
+      @orig_env[key] = value if key.start_with?("FLUENT_OJ_OPTION_")
+    end
+  end
+
+  teardown do
+    ENV.delete_if { |key| key.start_with?("FLUENT_OJ_OPTION_") }
+    @orig_env.each { |key, value| ENV[key] = value }
+  end
+
+  test "available?" do
+    assert_equal(@@oj_is_avaibale, Fluent::OjOptions.available?)
+  end
+
+  sub_test_case "set by environment variable" do
+    test "when no env vars set, returns default options" do
+      ENV.delete_if { |key| key.start_with?("FLUENT_OJ_OPTION_") }
+      defaults = Fluent::OjOptions::DEFAULTS
+      assert_equal(defaults, Fluent::OjOptions.load_env)
+      assert_equal(defaults, Oj.default_options.slice(*defaults.keys)) if @@oj_is_avaibale
+    end
+
+    test "valid env var passed with valid value, default is overridden" do
+      ENV["FLUENT_OJ_OPTION_BIGDECIMAL_LOAD"] = ":bigdecimal"
+      assert_equal(:bigdecimal, Fluent::OjOptions.load_env[:bigdecimal_load])
+      assert_equal(:bigdecimal, Oj.default_options[:bigdecimal_load]) if @@oj_is_avaibale
+    end
+
+    test "valid env var passed with invalid value, default is not overriden" do
+      ENV["FLUENT_OJ_OPTION_BIGDECIMAL_LOAD"] = ":conor"
+      assert_equal(:float, Fluent::OjOptions.load_env[:bigdecimal_load])
+      assert_equal(:float, Oj.default_options[:bigdecimal_load]) if @@oj_is_avaibale
+    end
+
+    test "invalid env var passed, nothing done with it" do
+      ENV["FLUENT_OJ_OPTION_CONOR"] = ":conor"
+      assert_equal(nil, Fluent::OjOptions.load_env[:conor])
+      assert_equal(nil, Oj.default_options[:conor]) if @@oj_is_avaibale
+    end
+  end
+end