diff --git a/src/main.rs b/src/main.rs
index 68ded3b..dff3001 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,5 @@
 use std::{
-    borrow::Cow, fs::File, io::{Read, Seek}, os::mikros::{ipc, syscalls, Errno}, path::PathBuf, sync::Arc
+    borrow::Cow, fs::File, io::{Read, Seek}, os::mikros::{ipc, syscalls, Errno, FileOpenMode}, path::PathBuf, sync::Arc
 };
 
 use parking_lot::RwLock;
@@ -37,7 +37,11 @@ impl fs_rpc::Server for Serv {
         Ok((self.mounts.read().len() - 1) as u64)
     }
 
-    fn open(&self, path: &std::path::Path, mount_id: u64) -> Result<(Option<u64>, u64), Errno> {
+    fn open(&self, path: &std::path::Path, mode: FileOpenMode, mount_id: u64) -> Result<(Option<u64>, u64), Errno> {
+        if !mode.readable() || mode.writable() {
+            // WRiting isn't supported yet, so the only sensible mode is readonly.
+            return Err(Errno::EACCES)
+        }
         let mounts = self.mounts.read();
         let mount = &mounts[mount_id as usize];
         let (&file_offset, &file_size) = mount