diff --git a/core/prelude-packages.el b/core/prelude-packages.el
index 8eec9dc..e2e8078 100644
--- a/core/prelude-packages.el
+++ b/core/prelude-packages.el
@@ -151,6 +151,7 @@ PACKAGE is installed only if not already present.  The file is opened in MODE."
     ("\\.ml\\'" tuareg tuareg-mode)
     ("\\.pp\\'" puppet-mode puppet-mode)
     ("\\.php\\'" php-mode php-mode)
+    ("\\.proto\\'" protobuf-mode protobuf-mode)
     ("PKGBUILD\\'" pkgbuild-mode pkgbuild-mode)
     ("\\.rs\\'" rust-mode rust-mode)
     ("\\.sass\\'" sass-mode sass-mode)