diff --git a/Cargo.toml b/Cargo.toml
index 67d5dcc..e935f86 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,3 +10,6 @@ edition = "2018"
 
 [lib]
 name = "syscall"
+
+[dependencies]
+bitflags = "1.1.0"
diff --git a/src/call.rs b/src/call.rs
index 8b56541..76e804f 100644
--- a/src/call.rs
+++ b/src/call.rs
@@ -1,6 +1,7 @@
 use super::arch::*;
 use super::data::{Map, SigAction, Stat, StatVfs, TimeSpec};
 use super::error::Result;
+use super::flag::*;
 use super::number::*;
 
 use core::{mem, ptr};
@@ -52,8 +53,8 @@ pub fn chmod<T: AsRef<[u8]>>(path: T, mode: usize) -> Result<usize> {
 }
 
 /// Produce a fork of the current process, or a new process thread
-pub unsafe fn clone(flags: usize) -> Result<usize> {
-    syscall1_clobber(SYS_CLONE, flags)
+pub unsafe fn clone(flags: CloneFlags) -> Result<usize> {
+    syscall1_clobber(SYS_CLONE, flags.bits())
 }
 
 /// Close a file
@@ -235,8 +236,8 @@ pub fn mkns(schemes: &[[usize; 2]]) -> Result<usize> {
 }
 
 /// Change mapping flags
-pub unsafe fn mprotect(addr: usize, size: usize, flags: usize) -> Result<usize> {
-    syscall3(SYS_MPROTECT, addr, size, flags)
+pub unsafe fn mprotect(addr: usize, size: usize, flags: MapFlags) -> Result<usize> {
+    syscall3(SYS_MPROTECT, addr, size, flags.bits())
 }
 
 /// Sleep for the time specified in `req`
@@ -274,8 +275,8 @@ pub unsafe fn physfree(physical_address: usize, size: usize) -> Result<usize> {
 /// # Errors
 ///
 /// * `EPERM` - `uid != 0`
-pub unsafe fn physmap(physical_address: usize, size: usize, flags: usize) -> Result<usize> {
-    syscall3(SYS_PHYSMAP, physical_address, size, flags)
+pub unsafe fn physmap(physical_address: usize, size: usize, flags: PhysmapFlags) -> Result<usize> {
+    syscall3(SYS_PHYSMAP, physical_address, size, flags.bits())
 }
 
 /// Unmap previously mapped physical memory
@@ -363,8 +364,8 @@ pub unsafe fn virttophys(virtual_address: usize) -> Result<usize> {
 }
 
 /// Check if a child process has exited or received a signal
-pub fn waitpid(pid: usize, status: &mut usize, options: usize) -> Result<usize> {
-    unsafe { syscall3(SYS_WAITPID, pid, status as *mut usize as usize, options) }
+pub fn waitpid(pid: usize, status: &mut usize, options: WaitFlags) -> Result<usize> {
+    unsafe { syscall3(SYS_WAITPID, pid, status as *mut usize as usize, options.bits()) }
 }
 
 /// Write a buffer to a file descriptor
diff --git a/src/data.rs b/src/data.rs
index 3b40727..7f952e2 100644
--- a/src/data.rs
+++ b/src/data.rs
@@ -1,11 +1,12 @@
 use core::ops::{Deref, DerefMut};
 use core::{mem, slice};
+use crate::flag::{EventFlags, ProtFlags, PtraceFlags, SigActionFlags};
 
 #[derive(Copy, Clone, Debug, Default)]
 #[repr(C)]
 pub struct Event {
     pub id: usize,
-    pub flags: usize,
+    pub flags: EventFlags,
     pub data: usize
 }
 
@@ -57,7 +58,7 @@ impl DerefMut for ITimerSpec {
 pub struct Map {
     pub offset: usize,
     pub size: usize,
-    pub flags: usize,
+    pub flags: ProtFlags,
 }
 
 impl Deref for Map {
@@ -112,7 +113,7 @@ impl DerefMut for Packet {
 pub struct SigAction {
     pub sa_handler: Option<extern "C" fn(usize)>,
     pub sa_mask: [u64; 2],
-    pub sa_flags: usize,
+    pub sa_flags: SigActionFlags,
 }
 
 #[allow(dead_code)]
@@ -306,7 +307,7 @@ impl DerefMut for FloatRegisters {
 #[derive(Clone, Copy, Debug, Default)]
 #[repr(C)]
 pub struct PtraceEvent {
-    pub cause: u64,
+    pub cause: PtraceFlags,
     pub a: usize,
     pub b: usize,
     pub c: usize,
diff --git a/src/flag.rs b/src/flag.rs
index dcc6550..77ac7e7 100644
--- a/src/flag.rs
+++ b/src/flag.rs
@@ -1,17 +1,58 @@
-pub const CLONE_VM: usize = 0x100;
-pub const CLONE_FS: usize = 0x200;
-pub const CLONE_FILES: usize = 0x400;
-pub const CLONE_SIGHAND: usize = 0x800;
-pub const CLONE_VFORK: usize = 0x4000;
-pub const CLONE_THREAD: usize = 0x10000;
-pub const CLONE_STACK: usize = 0x1000_0000;
+use bitflags::bitflags as inner_bitflags;
+
+macro_rules! bitflags {
+    (
+        $(#[$outer:meta])*
+        pub struct $BitFlags:ident: $T:ty {
+            $(
+                $(#[$inner:ident $($args:tt)*])*
+                const $Flag:ident = $value:expr;
+            )+
+        }
+    ) => {
+        // First, use the inner bitflags
+        inner_bitflags! {
+            #[derive(Default)]
+            $(#[$outer])*
+            pub struct $BitFlags: $T {
+                $(
+                    $(#[$inner $($args)*])*
+                    const $Flag = $value;
+                )+
+            }
+        }
+
+        // Secondly, re-export all inner constants
+        // (`pub use self::Struct::*` doesn't work)
+        $(
+            $(#[$inner $($args)*])*
+            pub const $Flag: $BitFlags = $BitFlags::$Flag;
+        )+
+    }
+}
+
+bitflags! {
+    pub struct CloneFlags: usize {
+        const CLONE_VM = 0x100;
+        const CLONE_FS = 0x200;
+        const CLONE_FILES = 0x400;
+        const CLONE_SIGHAND = 0x800;
+        const CLONE_VFORK = 0x4000;
+        const CLONE_THREAD = 0x10000;
+        const CLONE_STACK = 0x1000_0000;
+    }
+}
 
 pub const CLOCK_REALTIME: usize = 1;
 pub const CLOCK_MONOTONIC: usize = 4;
 
-pub const EVENT_NONE: usize = 0;
-pub const EVENT_READ: usize = 1;
-pub const EVENT_WRITE: usize = 2;
+bitflags! {
+    pub struct EventFlags: usize {
+        const EVENT_NONE = 0;
+        const EVENT_READ = 1;
+        const EVENT_WRITE = 2;
+    }
+}
 
 pub const F_DUPFD: usize = 0;
 pub const F_GETFD: usize = 1;
@@ -23,8 +64,12 @@ pub const FUTEX_WAIT: usize = 0;
 pub const FUTEX_WAKE: usize = 1;
 pub const FUTEX_REQUEUE: usize = 2;
 
-pub const MAP_SHARED: usize = 0x0001;
-pub const MAP_PRIVATE: usize = 0x0002;
+bitflags! {
+    pub struct MapFlags: usize {
+        const MAP_SHARED = 0x0001;
+        const MAP_PRIVATE = 0x0002;
+    }
+}
 
 pub const MODE_TYPE: u16 = 0xF000;
 pub const MODE_DIR: u16 = 0x4000;
@@ -56,29 +101,41 @@ pub const O_SYMLINK: usize =    0x4000_0000;
 pub const O_NOFOLLOW: usize =   0x8000_0000;
 pub const O_ACCMODE: usize =    O_RDONLY | O_WRONLY | O_RDWR;
 
-pub const PHYSMAP_WRITE: usize = 0x0000_0001;
-pub const PHYSMAP_WRITE_COMBINE: usize = 0x0000_0002;
-pub const PHYSMAP_NO_CACHE: usize = 0x0000_0004;
+bitflags! {
+    pub struct PhysmapFlags: usize {
+        const PHYSMAP_WRITE = 0x0000_0001;
+        const PHYSMAP_WRITE_COMBINE = 0x0000_0002;
+        const PHYSMAP_NO_CACHE = 0x0000_0004;
+    }
+}
 
 // The top 48 bits of PTRACE_* are reserved, for now
 
-pub const PTRACE_STOP_PRE_SYSCALL: u64 = 0x0000_0000_0000_0001;
-pub const PTRACE_STOP_POST_SYSCALL: u64 = 0x0000_0000_0000_0002;
-pub const PTRACE_STOP_SINGLESTEP: u64 = 0x0000_0000_0000_0004;
-pub const PTRACE_STOP_SIGNAL: u64 = 0x0000_0000_0000_0008;
-pub const PTRACE_STOP_MASK: u64 = 0x0000_0000_0000_00FF;
+bitflags! {
+    pub struct PtraceFlags: u64 {
+        const PTRACE_STOP_PRE_SYSCALL = 0x0000_0000_0000_0001;
+        const PTRACE_STOP_POST_SYSCALL = 0x0000_0000_0000_0002;
+        const PTRACE_STOP_SINGLESTEP = 0x0000_0000_0000_0004;
+        const PTRACE_STOP_SIGNAL = 0x0000_0000_0000_0008;
+        const PTRACE_STOP_MASK = 0x0000_0000_0000_00FF;
 
-pub const PTRACE_EVENT_CLONE: u64 = 0x0000_0000_0000_0100;
-pub const PTRACE_EVENT_MASK: u64 = 0x0000_0000_0000_0F00;
+        const PTRACE_EVENT_CLONE = 0x0000_0000_0000_0100;
+        const PTRACE_EVENT_MASK = 0x0000_0000_0000_0F00;
 
-pub const PTRACE_FLAG_SYSEMU: u64 = 0x0000_0000_0000_1000;
-pub const PTRACE_FLAG_WAIT: u64 = 0x0000_0000_0000_2000;
-pub const PTRACE_FLAG_MASK: u64 = 0x0000_0000_0000_F000;
+        const PTRACE_FLAG_SYSEMU = 0x0000_0000_0000_1000;
+        const PTRACE_FLAG_WAIT = 0x0000_0000_0000_2000;
+        const PTRACE_FLAG_MASK = 0x0000_0000_0000_F000;
+    }
+}
 
-pub const PROT_NONE: usize = 0x0000_0000;
-pub const PROT_EXEC: usize = 0x0001_0000;
-pub const PROT_WRITE: usize = 0x0002_0000;
-pub const PROT_READ: usize = 0x0004_0000;
+bitflags! {
+    pub struct ProtFlags: usize {
+        const PROT_NONE = 0x0000_0000;
+        const PROT_EXEC = 0x0001_0000;
+        const PROT_WRITE = 0x0002_0000;
+        const PROT_READ = 0x0004_0000;
+    }
+}
 
 pub const SEEK_SET: usize = 0;
 pub const SEEK_CUR: usize = 1;
@@ -123,18 +180,26 @@ pub const SIG_BLOCK: usize = 0;
 pub const SIG_UNBLOCK: usize = 1;
 pub const SIG_SETMASK: usize = 2;
 
-pub const SA_NOCLDSTOP: usize = 0x00000001;
-pub const SA_NOCLDWAIT: usize = 0x00000002;
-pub const SA_SIGINFO: usize =   0x00000004;
-pub const SA_RESTORER: usize =  0x04000000;
-pub const SA_ONSTACK: usize =   0x08000000;
-pub const SA_RESTART: usize =   0x10000000;
-pub const SA_NODEFER: usize =   0x40000000;
-pub const SA_RESETHAND: usize = 0x80000000;
+bitflags! {
+    pub struct SigActionFlags: usize {
+        const SA_NOCLDSTOP = 0x00000001;
+        const SA_NOCLDWAIT = 0x00000002;
+        const SA_SIGINFO =   0x00000004;
+        const SA_RESTORER =  0x04000000;
+        const SA_ONSTACK =   0x08000000;
+        const SA_RESTART =   0x10000000;
+        const SA_NODEFER =   0x40000000;
+        const SA_RESETHAND = 0x80000000;
+    }
+}
 
-pub const WNOHANG: usize =    0x01;
-pub const WUNTRACED: usize =  0x02;
-pub const WCONTINUED: usize = 0x08;
+bitflags! {
+    pub struct WaitFlags: usize {
+        const WNOHANG =    0x01;
+        const WUNTRACED =  0x02;
+        const WCONTINUED = 0x08;
+    }
+}
 
 /// True if status indicates the child is stopped.
 pub fn wifstopped(status: usize) -> bool {
diff --git a/src/scheme/generate.sh b/src/scheme/generate.sh
index e5d11ae..f95bf8a 100755
--- a/src/scheme/generate.sh
+++ b/src/scheme/generate.sh
@@ -11,7 +11,8 @@ echo "Generating SchemeBlock from Scheme"
 sed 's/trait Scheme/trait SchemeBlock/' scheme.rs \
 | sed 's/fn handle(\&self, packet: \&mut Packet)/fn handle(\&self, packet: \&Packet) -> Option<usize>/' \
 | sed 's/packet.a = Error::mux(res);/res.transpose().map(Error::mux)/' \
-| sed 's/Result<usize>/Result<Option<usize>>/g' \
+| sed 's/\.map(|f| f\.bits())/\.map(|f| f.map(|f| f.bits()))/' \
+| sed 's/Result<\([^>]\+\)>/Result<Option<\1>>/g' \
 > scheme_block.rs
 
 echo "Generating SchemeBlockMut from SchemeBlock"
diff --git a/src/scheme/scheme.rs b/src/scheme/scheme.rs
index 9777342..0c95a74 100644
--- a/src/scheme/scheme.rs
+++ b/src/scheme/scheme.rs
@@ -2,6 +2,7 @@ use core::{mem, slice};
 
 use crate::data::*;
 use crate::error::*;
+use crate::flag::*;
 use crate::number::*;
 
 pub trait Scheme {
@@ -19,7 +20,7 @@ pub trait Scheme {
             SYS_FCHMOD => self.fchmod(packet.b, packet.c as u16),
             SYS_FCHOWN => self.fchown(packet.b, packet.c as u32, packet.d as u32),
             SYS_FCNTL => self.fcntl(packet.b, packet.c, packet.d),
-            SYS_FEVENT => self.fevent(packet.b, packet.c),
+            SYS_FEVENT => self.fevent(packet.b, EventFlags::from_bits_truncate(packet.c)).map(|f| f.bits()),
             SYS_FMAP => if packet.d >= mem::size_of::<Map>() {
                 self.fmap(packet.b, unsafe { &*(packet.c as *const Map) })
             } else {
@@ -111,7 +112,7 @@ pub trait Scheme {
     }
 
     #[allow(unused_variables)]
-    fn fevent(&self, id: usize, flags: usize) -> Result<usize> {
+    fn fevent(&self, id: usize, flags: EventFlags) -> Result<EventFlags> {
         Err(Error::new(EBADF))
     }
 
diff --git a/src/scheme/scheme_block.rs b/src/scheme/scheme_block.rs
index 883fbef..4428eaa 100644
--- a/src/scheme/scheme_block.rs
+++ b/src/scheme/scheme_block.rs
@@ -2,6 +2,7 @@ use core::{mem, slice};
 
 use crate::data::*;
 use crate::error::*;
+use crate::flag::*;
 use crate::number::*;
 
 pub trait SchemeBlock {
@@ -19,7 +20,7 @@ pub trait SchemeBlock {
             SYS_FCHMOD => self.fchmod(packet.b, packet.c as u16),
             SYS_FCHOWN => self.fchown(packet.b, packet.c as u32, packet.d as u32),
             SYS_FCNTL => self.fcntl(packet.b, packet.c, packet.d),
-            SYS_FEVENT => self.fevent(packet.b, packet.c),
+            SYS_FEVENT => self.fevent(packet.b, EventFlags::from_bits_truncate(packet.c)).map(|f| f.map(|f| f.bits())),
             SYS_FMAP => if packet.d >= mem::size_of::<Map>() {
                 self.fmap(packet.b, unsafe { &*(packet.c as *const Map) })
             } else {
@@ -111,7 +112,7 @@ pub trait SchemeBlock {
     }
 
     #[allow(unused_variables)]
-    fn fevent(&self, id: usize, flags: usize) -> Result<Option<usize>> {
+    fn fevent(&self, id: usize, flags: EventFlags) -> Result<Option<EventFlags>> {
         Err(Error::new(EBADF))
     }
 
diff --git a/src/scheme/scheme_block_mut.rs b/src/scheme/scheme_block_mut.rs
index f4fa8c4..c4a49b3 100644
--- a/src/scheme/scheme_block_mut.rs
+++ b/src/scheme/scheme_block_mut.rs
@@ -2,6 +2,7 @@ use core::{mem, slice};
 
 use crate::data::*;
 use crate::error::*;
+use crate::flag::*;
 use crate::number::*;
 
 pub trait SchemeBlockMut {
@@ -19,7 +20,7 @@ pub trait SchemeBlockMut {
             SYS_FCHMOD => self.fchmod(packet.b, packet.c as u16),
             SYS_FCHOWN => self.fchown(packet.b, packet.c as u32, packet.d as u32),
             SYS_FCNTL => self.fcntl(packet.b, packet.c, packet.d),
-            SYS_FEVENT => self.fevent(packet.b, packet.c),
+            SYS_FEVENT => self.fevent(packet.b, EventFlags::from_bits_truncate(packet.c)).map(|f| f.map(|f| f.bits())),
             SYS_FMAP => if packet.d >= mem::size_of::<Map>() {
                 self.fmap(packet.b, unsafe { &*(packet.c as *const Map) })
             } else {
@@ -111,7 +112,7 @@ pub trait SchemeBlockMut {
     }
 
     #[allow(unused_variables)]
-    fn fevent(&mut self, id: usize, flags: usize) -> Result<Option<usize>> {
+    fn fevent(&mut self, id: usize, flags: EventFlags) -> Result<Option<EventFlags>> {
         Err(Error::new(EBADF))
     }
 
diff --git a/src/scheme/scheme_mut.rs b/src/scheme/scheme_mut.rs
index fd52592..eea1331 100644
--- a/src/scheme/scheme_mut.rs
+++ b/src/scheme/scheme_mut.rs
@@ -2,6 +2,7 @@ use core::{mem, slice};
 
 use crate::data::*;
 use crate::error::*;
+use crate::flag::*;
 use crate::number::*;
 
 pub trait SchemeMut {
@@ -19,7 +20,7 @@ pub trait SchemeMut {
             SYS_FCHMOD => self.fchmod(packet.b, packet.c as u16),
             SYS_FCHOWN => self.fchown(packet.b, packet.c as u32, packet.d as u32),
             SYS_FCNTL => self.fcntl(packet.b, packet.c, packet.d),
-            SYS_FEVENT => self.fevent(packet.b, packet.c),
+            SYS_FEVENT => self.fevent(packet.b, EventFlags::from_bits_truncate(packet.c)).map(|f| f.bits()),
             SYS_FMAP => if packet.d >= mem::size_of::<Map>() {
                 self.fmap(packet.b, unsafe { &*(packet.c as *const Map) })
             } else {
@@ -111,7 +112,7 @@ pub trait SchemeMut {
     }
 
     #[allow(unused_variables)]
-    fn fevent(&mut self, id: usize, flags: usize) -> Result<usize> {
+    fn fevent(&mut self, id: usize, flags: EventFlags) -> Result<EventFlags> {
         Err(Error::new(EBADF))
     }