diff --git a/ChangeLog b/ChangeLog
index 60ed1d1d97..292853481c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Tue Oct 16 10:54:03 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Tue Oct 16 11:27:04 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* file.c (rb_file_join): check nul-byte only for strings, since
+	  FilePathStringValue() does it.  [ruby-core:48012] [Bug #7168]
 
 	* file.c (rb_file_join): path names must be ASCII-compatible.
 	  [ruby-core:48012] [Bug #7168]
diff --git a/file.c b/file.c
index f4ae1bb155..8ffd874a9c 100644
--- a/file.c
+++ b/file.c
@@ -3941,6 +3941,7 @@ rb_file_join(VALUE ary, VALUE sep)
 	tmp = RARRAY_PTR(ary)[i];
 	switch (TYPE(tmp)) {
 	  case T_STRING:
+	    StringValueCStr(tmp);
 	    break;
 	  case T_ARRAY:
 	    if (ary == tmp) {
@@ -3957,8 +3958,7 @@ rb_file_join(VALUE ary, VALUE sep)
 	  default:
 	    FilePathStringValue(tmp);
 	}
-	name = StringValueCStr(result);
-	len = RSTRING_LEN(result);
+	RSTRING_GETMEM(result, name, len);
 	if (i == 0) {
 	    rb_enc_copy(result, tmp);
 	}
diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
index f697488192..10d04ddf15 100644
--- a/test/ruby/test_file_exhaustive.rb
+++ b/test/ruby/test_file_exhaustive.rb
@@ -793,6 +793,18 @@ class TestFileExhaustive < Test::Unit::TestCase
     bug7168 = '[ruby-core:48012]'
     names = %w"a b".map {|s| s.encode(Encoding::UTF_16LE)}
     assert_raise(Encoding::CompatibilityError, bug7168) {File.join(*names)}
+    assert_raise(Encoding::CompatibilityError, bug7168) {File.join(names)}
+
+    a = Object.new
+    b = names[1]
+    names = [a, "b"]
+    a.singleton_class.class_eval do
+      define_method(:to_path) do
+        names[1] = b
+        "a"
+      end
+    end
+    assert_raise(Encoding::CompatibilityError, bug7168) {File.join(names)}
   end
 
   def test_truncate