diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 07c6143af3bf27..2f82c2900cde45 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -12,6 +12,11 @@ def quote
     /\s/ =~ self ? "\"#{self}\"" : "#{self}"
   end
 
+  # Escape whitespaces for Makefile.
+  def unspace
+    gsub(/\s/, '\\\\\\&')
+  end
+
   # Generates a string used as cpp macro name.
   def tr_cpp
     strip.upcase.tr_s("^A-Z0-9_*", "_").tr_s("*", "P")
@@ -196,10 +201,11 @@ def map_dir(dir, map = nil)
   $extmk = path[0, topdir.size+1] == topdir+"/"
   $extmk &&= %r"\A(?:ext|enc|tool|test(?:/.+)?)\z" =~ File.dirname(path[topdir.size+1..-1])
   $extmk &&= true
-  if not $extmk and File.exist?(($hdrdir = RbConfig::CONFIG["rubyhdrdir"]) + "/ruby/ruby.h")
+  if not $extmk and File.exist?(RbConfig::CONFIG["rubyhdrdir"] + "/ruby/ruby.h")
+    $hdrdir = CONFIG["rubyhdrdir"]
     $topdir = $hdrdir
     $top_srcdir = $hdrdir
-    $arch_hdrdir = $hdrdir + "/$(arch)"
+    $arch_hdrdir = "$(hdrdir)/$(arch)"
   elsif File.exist?(($hdrdir = ($top_srcdir ||= topdir) + "/include")  + "/ruby.h")
     $topdir ||= RbConfig::CONFIG["topdir"]
     $arch_hdrdir = "$(extout)/include/$(arch)"
@@ -1722,7 +1728,7 @@ def mkintpath(path)
   end
   unless defined?(mkintpath)
     def mkintpath(path)
-      path
+      path.unspace
     end
   end
 
@@ -1750,9 +1756,9 @@ def configuration(srcdir)
 
 #### Start of system configuration section. ####
 #{"top_srcdir = " + $top_srcdir.sub(%r"\A#{Regexp.quote($topdir)}/", "$(topdir)/") if $extmk}
-srcdir = #{srcdir.gsub(/\$\((srcdir)\)|\$\{(srcdir)\}/) {mkintpath(CONFIG[$1||$2])}.quote}
-topdir = #{mkintpath($extmk ? CONFIG["topdir"] : $topdir).quote}
-hdrdir = #{mkintpath(CONFIG["hdrdir"]).quote}
+srcdir = #{srcdir.gsub(/\$\((srcdir)\)|\$\{(srcdir)\}/) {mkintpath(CONFIG[$1||$2])}}
+topdir = #{mkintpath($extmk ? CONFIG["topdir"] : $topdir)}
+hdrdir = #{mkintpath(CONFIG["hdrdir"])}
 arch_hdrdir = #{$arch_hdrdir.quote}
 VPATH = #{vpath.join(CONFIG['PATH_SEPARATOR'])}
 }
@@ -1764,7 +1770,7 @@ def configuration(srcdir)
     end
     CONFIG.each do |key, var|
       next unless /prefix$/ =~ key
-      mk << "#{key} = #{with_destdir(var)}\n"
+      mk << "#{key} = #{with_destdir(var).unspace}\n"
     end
     CONFIG.each do |key, var|
       next if /^abs_/ =~ key
@@ -2126,14 +2132,14 @@ def create_makefile(target, srcprefix = nil)
     if target
       f = "$(DLLIB)"
       dest = "#{dir}/#{f}"
-      mfile.puts dest
       if $extout
+        mfile.puts dest
         mfile.print "clean-so::\n"
         mfile.print "\t-$(Q)$(RM) #{fseprepl[dest]}\n"
         mfile.print "\t-$(Q)$(RMDIRS) #{fseprepl[dir]}#{$ignore_error}\n"
       else
-        mfile.print "#{dest}: #{f}\n\t-$(Q)$(MAKEDIRS) $(@D#{sep})\n"
-        mfile.print "\t$(INSTALL_PROG) #{fseprepl[f]} $(@D#{sep})\n"
+        mfile.print "#{f} #{timestamp_file(dir)}\n"
+        mfile.print "\t$(INSTALL_PROG) #{fseprepl[f]} #{dir}\n"
         if defined?($installed_list)
           mfile.print "\t@echo #{dir}/#{File.basename(f)}>>$(INSTALLED_LIST)\n"
         end
@@ -2398,7 +2404,7 @@ def mkmf_failed(path)
       "$(LDSHARED) #{OUTFLAG}$@ $(OBJS) " \
       "$(LIBPATH) $(DLDFLAGS) $(LOCAL_LIBS) $(LIBS)"
     end
-  LIBPATHFLAG = config_string('LIBPATHFLAG') || ' -L"%s"'
+  LIBPATHFLAG = config_string('LIBPATHFLAG') || ' -L%s'
   RPATHFLAG = config_string('RPATHFLAG') || ''
   LIBARG = config_string('LIBARG') || '-l%s'
   MAIN_DOES_NOTHING = config_string('MAIN_DOES_NOTHING') || 'int main(void) {return 0;}'