diff --git a/common.mk b/common.mk
index 25937135d7..8182eb7865 100644
--- a/common.mk
+++ b/common.mk
@@ -224,10 +224,9 @@ mjit_config.h: Makefile
 # Other `-Dxxx`s preceding `-DMJIT_HEADER` will be removed in transform_mjit_header.rb.
 # So `-DMJIT_HEADER` should be passed first when rb_mjit_header.h is generated.
 $(TIMESTAMPDIR)/$(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).time: probes.h vm.$(OBJEXT) \
-		$(TIMESTAMPDIR)/$(arch)/.time $(srcdir)/tool/run_without_tabs.rb
+		$(TIMESTAMPDIR)/$(arch)/.time
 	$(ECHO) building $(@F:.time=.h)
-	$(Q) $(BASERUBY) $(srcdir)/tool/run_without_tabs.rb \
-		$(CPP) -DMJIT_HEADER $(MJIT_HEADER_FLAGS) $(CFLAGS) $(XCFLAGS) $(CPPFLAGS) $(srcdir)/vm.c $(CPPOUTFLAG)$(@F:.time=.h).new
+	$(Q) $(CPP) -DMJIT_HEADER $(MJIT_HEADER_FLAGS) $(CFLAGS) $(XCFLAGS) $(CPPFLAGS) $(srcdir)/vm.c $(CPPOUTFLAG)$(@F:.time=.h).new
 	$(Q) $(IFCHANGE) "--timestamp=$@" $(@F:.time=.h) $(@F:.time=.h).new
 
 $(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).h: $(TIMESTAMPDIR)/$(MJIT_HEADER:.h=)$(MJIT_HEADER_SUFFIX).time
diff --git a/tool/run_without_tabs.rb b/tool/run_without_tabs.rb
deleted file mode 100644
index 0ac21f90ce..0000000000
--- a/tool/run_without_tabs.rb
+++ /dev/null
@@ -1,35 +0,0 @@
-# frozen_string_literal: true
-# This is a script to run a command in ARGV, expanding tabs in some files
-# included by vm.c to normalize indentation of MJIT header.
-#
-# Note that preprocessor of GCC converts a hard tab to one spaces, where
-# we expect it to be shown as 8 spaces. To obviate this script, we need
-# to convert all tabs to spaces in these files.
-
-require 'fileutils'
-
-srcdir = File.expand_path('..', __dir__)
-targets = Dir.glob(File.join(srcdir, 'vm*.*'))
-sources = {}
-mtimes = {}
-
-targets.each do |target|
-  sources[target] = File.read(target)
-  mtimes[target] = File.mtime(target)
-
-  expanded = sources[target].gsub(/^\t+/) { |tab| ' ' * 8 * tab.length }
-  if sources[target] == expanded
-    puts "#{target.dump} has no hard tab indentation. This should be ignored in tool/run_without_tabs.rb."
-  end
-  File.write(target, expanded)
-  FileUtils.touch(target, mtime: mtimes[target])
-end
-
-result = system(*ARGV)
-
-targets.each do |target|
-  File.write(target, sources.fetch(target))
-  FileUtils.touch(target, mtime: mtimes.fetch(target))
-end
-
-exit result