diff --git a/redox-rt/src/sys.rs b/redox-rt/src/sys.rs
index 45779f6b89..2f9bd82c30 100644
--- a/redox-rt/src/sys.rs
+++ b/redox-rt/src/sys.rs
@@ -1,4 +1,7 @@
-use core::ptr::addr_of;
+use core::{
+    ptr::addr_of,
+    sync::atomic::{AtomicU32, Ordering},
+};
 
 use syscall::{
     error::{Error, Result, EINTR},
@@ -114,3 +117,20 @@ pub fn posix_kill_thread(thread_fd: usize, signal: u32) -> Result<()> {
         Err(error) => Err(error),
     }
 }
+
+static UMASK: AtomicU32 = AtomicU32::new(0o022);
+
+/// Controls the set of bits removed from the `mode` mask when new file descriptors are created.
+///
+/// Must be validated by the caller
+//
+// TODO: validate here?
+#[inline]
+pub fn swap_umask(mask: u32) -> u32 {
+    UMASK.swap(mask, Ordering::AcqRel)
+}
+
+#[inline]
+pub fn get_umask() -> u32 {
+    UMASK.load(Ordering::Acquire)
+}
diff --git a/src/header/signal/mod.rs b/src/header/signal/mod.rs
index a8785a8807..61e1780f5b 100644
--- a/src/header/signal/mod.rs
+++ b/src/header/signal/mod.rs
@@ -5,8 +5,8 @@ use core::{mem, ptr};
 use cbitset::BitSet;
 
 use crate::{
-    error::{Errno, ResultExt},
     c_str::CStr,
+    error::{Errno, ResultExt},
     header::{errno, time::timespec},
     platform::{self, types::*, Pal, PalSignal, Sys},
 };
diff --git a/src/platform/redox/mod.rs b/src/platform/redox/mod.rs
index 57482b4d9b..62e90f61cb 100644
--- a/src/platform/redox/mod.rs
+++ b/src/platform/redox/mod.rs
@@ -8,7 +8,7 @@ use syscall::{
     self,
     data::{Map, Stat as redox_stat, StatVfs as redox_statvfs, TimeSpec as redox_timespec},
     dirent::{DirentHeader, DirentKind},
-    Error, PtraceEvent, Result, EMFILE,
+    Error, PtraceEvent, Result, EMFILE, MODE_PERM,
 };
 
 use crate::{
@@ -25,7 +25,7 @@ use crate::{
         sys_mman::{MAP_ANONYMOUS, MAP_FAILED, PROT_READ, PROT_WRITE},
         sys_random,
         sys_resource::{rlimit, rusage, RLIM_INFINITY},
-        sys_stat::{stat, S_ISGID, S_ISUID},
+        sys_stat::{stat, S_ISGID, S_ISUID, S_ISVTX},
         sys_statvfs::statvfs,
         sys_time::{timeval, timezone},
         sys_utsname::{utsname, UTSLENGTH},
@@ -784,7 +784,16 @@ impl Pal for Sys {
     fn open(path: CStr, oflag: c_int, mode: mode_t) -> Result<c_int, Errno> {
         let path = path.to_str().map_err(|_| Errno(EINVAL))?;
 
-        Ok(libredox::open(path, oflag, mode)? as c_int)
+        // POSIX states that umask should affect the following:
+        //
+        // open, openat (TODO), creat, mkdir, mkdirat (TODO),
+        // mkfifo, mkfifoat (TODO), mknod, mknodat (TODO),
+        // mq_open, and sem_open,
+        //
+        // all of which (the ones that exist thus far) currently call this function.
+        let effective_mode = mode & !(redox_rt::sys::get_umask() as mode_t);
+
+        Ok(libredox::open(path, oflag, effective_mode)? as c_int)
     }
 
     fn pipe2(fds: &mut [c_int], flags: c_int) -> c_int {
@@ -966,7 +975,8 @@ impl Pal for Sys {
     }
 
     fn umask(mask: mode_t) -> mode_t {
-        e(syscall::umask(mask as usize)) as mode_t
+        let new_effective_mask = mask & mode_t::from(MODE_PERM) & !S_ISVTX;
+        (redox_rt::sys::swap_umask(new_effective_mask as u32) as mode_t) & !S_ISVTX
     }
 
     fn uname(utsname: *mut utsname) -> c_int {
diff --git a/src/platform/redox/path.rs b/src/platform/redox/path.rs
index 414056a63c..9d6739a463 100644
--- a/src/platform/redox/path.rs
+++ b/src/platform/redox/path.rs
@@ -130,6 +130,7 @@ pub fn clone_default_scheme() -> Option<Box<str>> {
     DEFAULT_SCHEME.lock().clone()
 }
 
+// TODO: Move to redox-rt, or maybe part of it?
 pub fn open(path: &str, flags: usize) -> Result<usize> {
     // TODO: SYMLOOP_MAX
     const MAX_LEVEL: usize = 64;