diff --git a/ChangeLog b/ChangeLog
index 2fae9ad137..ad940f3313 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Mar 15 15:02:58 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* file.c (ruby_enc_find_basename): allow NULL as alllen.
+	  [ruby-dev:45363][Bug #6146]
+
 Thu Mar 15 14:49:31 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (rb_str_conv_enc_opts): default to original encoding.
diff --git a/file.c b/file.c
index 1869a29c3b..49032957d0 100644
--- a/file.c
+++ b/file.c
@@ -3563,7 +3563,7 @@ ruby_enc_find_basename(const char *name, long *baselen, long *alllen, rb_encodin
 #endif
     long f = 0, n = -1;
 
-    end = name + *alllen;
+    end = name + (alllen ? (size_t)*alllen : strlen(name));
     name = skipprefix(name, end, enc);
 #if defined DOSISH_DRIVE_LETTER || defined DOSISH_UNC
     root = name;