diff --git a/lib/fluent/env.rb b/lib/fluent/env.rb
index 33aaa7223c..75540c346b 100644
--- a/lib/fluent/env.rb
+++ b/lib/fluent/env.rb
@@ -35,10 +35,10 @@ def self.windows?
   end
 
   def self.linux?
-    /linux/ === RUBY_PLATFORM
+    RUBY_PLATFORM.include?("linux")
   end
 
   def self.macos?
-    /darwin/ =~ RUBY_PLATFORM
+    RUBY_PLATFORM.include?("darwin")
   end
 end
diff --git a/lib/fluent/plugin/in_tail.rb b/lib/fluent/plugin/in_tail.rb
index 221c5e2f60..3c182e06f3 100644
--- a/lib/fluent/plugin/in_tail.rb
+++ b/lib/fluent/plugin/in_tail.rb
@@ -184,7 +184,7 @@ def configure(conf)
       configure_tag
       configure_encoding
 
-      @multiline_mode = parser_config["@type"] =~ /multiline/
+      @multiline_mode = parser_config["@type"].include?("multiline")
       @receive_handler = if @multiline_mode
                            method(:parse_multilines)
                          else