diff --git a/oni-csharp/oni-csharp.el b/oni-csharp/oni-csharp.el
index 1eb20a4..8451d93 100644
--- a/oni-csharp/oni-csharp.el
+++ b/oni-csharp/oni-csharp.el
@@ -4,7 +4,7 @@
 
 ;; Author: Tom Willemse <tom@ryuslash.org>
 ;; Keywords: local
-;; Version: 2022.0202.115001
+;; Version: 2023.0525.001714
 ;; Package-Requires: (csharp-mode oni-company oni-flycheck oni-yasnippet oni-hydra oni-lsp oni-smartparens)
 
 ;; This program is free software; you can redistribute it and/or modify
@@ -223,5 +223,37 @@ _cs_: Solution
 ;;;###autoload
 (add-to-list 'auto-mode-alist `(,(rx ".sln" eos) . csharp-solution-mode))
 
+(defun oni-csharp-add-file-to-project ()
+  (interactive)
+  (let* ((file-name (buffer-file-name))
+         (project-dir (locate-dominating-file file-name
+                                              (lambda (file)
+                                                (if (file-directory-p file)
+                                                    (directory-files file nil (rx ".csproj" eos))
+                                                  (string-suffix-p ".csproj" file)))))
+         (project-files (directory-files project-dir nil (rx ".csproj" eos)))
+         (project-file (cl-case (length project-files)
+                         (0 (error "No project files found in %s" project-dir))
+                         (1 (car project-files))
+                         (t (completing-read "Which project file? " project-files))))
+         (relative-file-name (file-relative-name file-name project-dir))
+         (project-file-absolute-path (expand-file-name project-file project-dir)))
+    (with-current-buffer (find-file-noselect project-file-absolute-path)
+      (save-excursion
+        (re-search-forward (rx "<Compile"))
+        (end-of-line)
+        (when (and buffer-file-read-only
+                   (vc-registered project-file-absolute-path))
+          (vc-checkout project-file-absolute-path))
+        (insert "\n" "<Compile Include=\"" (string-replace "/" "\\" relative-file-name) "\" />")
+        (re-search-backward (rx "<ItemGroup>"))
+        (forward-line)
+        (let ((start (line-beginning-position)))
+          (re-search-forward (rx "</ItemGroup>"))
+          (forward-line -1)
+          (indent-region start (line-end-position))
+          (sort-lines nil start (line-end-position)))
+        (save-buffer)))))
+
 (provide 'oni-csharp)
 ;;; oni-csharp.el ends here