diff --git a/plugins/destinations/file.inc b/plugins/destinations/file.inc
index 616606f..1586f09 100644
--- a/plugins/destinations/file.inc
+++ b/plugins/destinations/file.inc
@@ -260,12 +260,60 @@ class MigrateDestinationFile extends MigrateDestinationEntity {
     }
 
     migrate_instrument_start('file_save');
-    if (!file_load_multiple(array(), array('uri' => $file->uri))) {
-      // Get this orphaned file into the file table.
-      $file->fid = NULL;
-      $file->status |= FILE_STATUS_PERMANENT; // Save a write in file_field_presave().
+
+    // Look for existing files
+    $existing_by_uri = file_load_multiple(array(), array('uri' => $file->uri));
+    if (!empty($existing_by_uri)) {
+      $conflict_fid = reset($existing_by_uri)->fid;
     }
-    $file = file_save($file);
+    // TODO:
+    //   We already load $old_file above, but only for Migration::DESTINATION.
+    $old_file = file_load($file->fid);
+    if (empty($file->fid)) {
+      // We are creating a new file entity.
+      if (isset($conflict_fid)) {
+        // Another file entity does already exist, which refers to the same physical file.
+        // -> dedupe the uri!
+        // In fact, we should have done this before already.
+        // So, we rather throw an exception.
+        throw new MigrateException(t('Trying to create a new file entity for an already-existing physical file location.'));
+      }
+      else {
+        // We are safe to create a new file.
+        $file->status |= FILE_STATUS_PERMANENT; // Save a write in file_field_presave().
+        $file = file_save($file);
+      }
+    }
+    elseif (empty($old_file)) {
+      // Trying to save a file with explicit fid,
+      // but there is no existing entity to overwrite.
+      // Do we allow this?
+    }
+    else {
+      // This is an update.
+      if ($old_file->uri === $file->uri) {
+        // uri has not changed, but the file contents might have.
+        // At least, we don't need to be afraid of conflicts with other file entities.
+        // In fact, we assume most of the work to be already done.
+        $file->status |= FILE_STATUS_PERMANENT; // Save a write in file_field_presave().
+        $file = file_save($file);
+      }
+      elseif (isset($conflict_fid)) {
+        // Another file entity does already exist, with the same file location (uri).
+        // -> dedupe the uri!
+        // In fact, we should have done this before already.
+        // So, we rather throw an exception.
+        throw new MigrateException(t('Trying to update a file entity with an uri that is already occupied.'));
+      }
+      else {
+        // uri has changed. file contents might have changed.
+        // Delete the old one, create the new file, update the uri.
+        // In fact, we assume this has already happened.
+        $file->status |= FILE_STATUS_PERMANENT; // Save a write in file_field_presave().
+        $file = file_save($file);
+      }
+    }
+
     migrate_instrument_stop('file_save');
     $this->complete($file, $row);