diff --git a/ChangeLog b/ChangeLog
index 1a5dc2afa4..49b0d11c3c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Sep  3 15:32:44 2006  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb: get rid of nil.to_s.
+
 Sun Sep  3 06:24:38 2006  Tanaka Akira  <akr@fsij.org>
 
 	* ext/socket/socket.c (ruby_connect): sockerrlen should be socklen_t.
@@ -27,7 +31,7 @@ Sat Sep  2 23:53:28 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
 	* parse.y (rb_intern2): handle symbol as strings.
 
 	* string.c (str_new): substring of symbols are mere strings, not
-	  symbols. 
+	  symbols.
 
 Sat Sep  2 23:37:29 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
@@ -36,7 +40,7 @@ Sat Sep  2 23:37:29 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
 	  (RARRAY_PTR): ditto.
 
 	* array.c: use RARRAY_LEN and RARRAY_PTR.
-	
+
 Sat Sep  2 13:23:01 2006  Tanaka Akira  <akr@fsij.org>
 
 	* common.mk (ia64.o): use the compiler driver to assemble ia64.s
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 173c1981c2..a09d8d7cab 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -536,7 +536,7 @@ end
 
 def checking_for(m, fmt = nil)
   f = caller[0][/in `(.*)'$/, 1] and f << ": " #` for vim
-  m = "checking #{'for ' if /\Acheck/ !~ f}#{m}... "
+  m = "checking #{/\Acheck/ =~ f ? '' : 'for '}#{m}... "
   message "%s", m
   a = r = nil
   Logging::postpone do
@@ -1099,7 +1099,7 @@ COPY = #{config_string('CP') || '@$(RUBY) -run -e cp -- -v'}
 
 #### End of system configuration section. ####
 
-preload = #{$preload.join(" ") if $preload}
+preload = #{$preload ? $preload.join(' ') : ''}
 }
   if $nmake == ?b
     mk.each do |x|
@@ -1456,7 +1456,7 @@ MESSAGE
 
 def mkmf_failed(path)
   unless $makefile_created or File.exist?("Makefile")
-    opts = $arg_config.collect {|t, n| "\t#{t}#{"=#{n}" if n}\n"}
+    opts = $arg_config.collect {|t, n| "\t#{t}#{n ? "=#{n}" : ""}\n"}
     abort "*** #{path} failed ***\n" + FailedMessage + opts.join
   end
 end
@@ -1502,7 +1502,7 @@ end
 config_string('COMMON_HEADERS') do |s|
   Shellwords.shellwords(s).each {|s| hdr << "#include <#{s}>"}
 end
-COMMON_HEADERS = if hdr.empty? then "" else hdr.join("\n") end
+COMMON_HEADERS = hdr.join("\n")
 COMMON_LIBS = config_string('COMMON_LIBS', &split) || []
 
 COMPILE_RULES = config_string('COMPILE_RULES', &split) || %w[.%s.%s:]