diff --git a/common.mk b/common.mk
index db930426a3..74463651e1 100755
--- a/common.mk
+++ b/common.mk
@@ -785,9 +785,9 @@ extconf: $(PREP)
 
 $(RBCONFIG): $(srcdir)/tool/mkconfig.rb config.status $(srcdir)/version.h
 	$(Q)$(BOOTSTRAPRUBY) -n \
-	-e 'BEGIN{VERSION=ARGV.shift;MIS=ARGV.dup}' \
-	-e 'END{abort "UNICODE version mismatch: #{MIS}" unless MIS.empty?}' \
-	-e '(MIS.delete(ARGF.path); ARGF.close) if /ONIG_UNICODE_VERSION_STRING +"#{Regexp.quote(VERSION)}"/o' \
+	-e 'BEGIN{version=ARGV.shift;mis=ARGV.dup}' \
+	-e 'END{abort "UNICODE version mismatch: #{mis}" unless mis.empty?}' \
+	-e '(mis.delete(ARGF.path); ARGF.close) if /ONIG_UNICODE_VERSION_STRING +"#{Regexp.quote(version)}"/o' \
 	$(UNICODE_VERSION) $(UNICODE_DATA_HEADERS)
 	$(Q)$(BOOTSTRAPRUBY) $(srcdir)/tool/mkconfig.rb \
 		-arch=$(arch) -version=$(RUBY_PROGRAM_VERSION) \
diff --git a/tool/colorize.rb b/tool/colorize.rb
index 92076b9928..1cbbeef543 100644
--- a/tool/colorize.rb
+++ b/tool/colorize.rb
@@ -4,7 +4,7 @@ class Colorize
   def initialize(color = nil)
     @colors = @reset = nil
     if color or (color == nil && STDOUT.tty?)
-      if (/\A\e\[.*m\z/ =~ IO.popen("tput smso", "r", :err => IO::NULL, &:read) rescue nil)
+      if (/\A\e\[.*m\z/ =~ IO.popen("tput smso", "r", err: IO::NULL, &:read) rescue nil)
         @beg = "\e["
         @colors = (colors = ENV['TEST_COLORS']) ? Hash[colors.scan(/(\w+)=([^:\n]*)/)] : {}
         @reset = "#{@beg}m"
diff --git a/tool/downloader.rb b/tool/downloader.rb
index 2436a4dae7..f42f9a0ef1 100644
--- a/tool/downloader.rb
+++ b/tool/downloader.rb
@@ -173,7 +173,7 @@ class Downloader
       if cache_save
         save_cache(cache, file, name)
       end
-      return file.respond_to?(:to_path) ? file.to_path : file.to_s
+      return file.to_path
     end
     if dryrun
       puts "Download #{url} into #{file}"
diff --git a/tool/generic_erb.rb b/tool/generic_erb.rb
index 456a8e138b..3904b570c4 100644
--- a/tool/generic_erb.rb
+++ b/tool/generic_erb.rb
@@ -33,9 +33,8 @@ unchanged = color.pass("unchanged")
 updated = color.fail("updated")
 
 result = templates.map do |template|
-  method = ERB.instance_method(:initialize)
-  if method.respond_to?(:parameters) && method.parameters.assoc(:key) # Ruby 2.6+
-    erb = ERB.new(File.read(template), :trim_mode => '%-')
+  if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+    erb = ERB.new(File.read(template), trim_mode: '%-')
   else
     erb = ERB.new(File.read(template), nil, '%-')
   end