diff --git a/core/includes/file.inc b/core/includes/file.inc
index 788f213..d9ac6e6 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -598,6 +598,9 @@ function file_valid_uri($uri) {
  *   is reported.
  * - If file already exists in $destination either the call will error out,
  *   replace the file or rename the file based on the $replace parameter.
+ * - If the $source and $destination are equal, the behaviour depends on the
+ *   $replace parameter. FILE_EXIST_REPLACE will error out. FILE_EXIST_RENAME
+ *   will rename the file until the $destination is unique.
  * - Provides a fallback using realpaths if the move fails using stream
  *   wrappers. This can occur because PHP's copy() function does not properly
  *   support streams if safe_mode or open_basedir are enabled. See
diff --git a/core/modules/file/file.module b/core/modules/file/file.module
index 16ce43f..9e9f19f 100644
--- a/core/modules/file/file.module
+++ b/core/modules/file/file.module
@@ -134,10 +134,11 @@ function file_usage() {
  * stored in the database. This is a powerful function that in many ways
  * performs like an advanced version of copy().
  * - Checks if $source and $destination are valid and readable/writable.
- * - Checks that $source is not equal to $destination; if they are an error
- *   is reported.
  * - If file already exists in $destination either the call will error out,
  *   replace the file or rename the file based on the $replace parameter.
+ * - If the $source and $destination are equal, the behaviour depends on the
+ *   $replace parameter. FILE_EXIST_REPLACE will error out. FILE_EXIST_RENAME
+ *   will rename the file until the $destination is unique.
  * - Adds the new file to the files database. If the source file is a
  *   temporary file, the resulting file will also be a temporary file. See
  *   file_save_upload() for details on temporary files.