diff --git a/crates/sel4/bitfield-types/src/lib.rs b/crates/sel4/bitfield-types/src/lib.rs
index c8caef60a..e4fc6c4fa 100644
--- a/crates/sel4/bitfield-types/src/lib.rs
+++ b/crates/sel4/bitfield-types/src/lib.rs
@@ -231,47 +231,6 @@ where
 
 // // //
 
-#[repr(C)]
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
-pub struct Bitfield<T, const N: usize> {
-    arr: [T; N],
-}
-
-impl<T, const N: usize> Bitfield<T, N>
-where
-    T: UnsignedPrimInt,
-{
-    pub fn from_arr(arr: [T; N]) -> Self {
-        Self { arr }
-    }
-
-    pub fn into_arr(self) -> [T; N] {
-        self.arr
-    }
-
-    pub fn as_arr(&self) -> &[T; N] {
-        &self.arr
-    }
-
-    pub fn as_mut_arr(&mut self) -> &mut [T; N] {
-        &mut self.arr
-    }
-
-    pub fn zeroed() -> Self {
-        Self::from_arr([T::zero(); N])
-    }
-
-    pub fn get_bits(&self, range: Range<usize>) -> T {
-        get_bits(&self.arr, range)
-    }
-
-    pub fn set_bits(&mut self, range: Range<usize>, bits: T) {
-        set_bits(&mut self.arr, range, bits)
-    }
-}
-
-// // //
-
 #[cfg(test)]
 mod test {
     #![allow(unused_imports)]
diff --git a/crates/sel4/sys/src/bf.rs b/crates/sel4/sys/src/bf/mod.rs
similarity index 73%
rename from crates/sel4/sys/src/bf.rs
rename to crates/sel4/sys/src/bf/mod.rs
index 1c9e08188..bdc8bf272 100644
--- a/crates/sel4/sys/src/bf.rs
+++ b/crates/sel4/sys/src/bf/mod.rs
@@ -1,6 +1,8 @@
 use core::fmt;
 
-use sel4_bitfield_types::Bitfield;
+pub(crate) mod types;
+
+use types::Bitfield;
 
 include!(concat!(env!("OUT_DIR"), "/types.rs"));
 include!(concat!(env!("OUT_DIR"), "/shared_types.rs"));
diff --git a/crates/sel4/sys/src/bf/types.rs b/crates/sel4/sys/src/bf/types.rs
new file mode 100644
index 000000000..306dd044e
--- /dev/null
+++ b/crates/sel4/sys/src/bf/types.rs
@@ -0,0 +1,42 @@
+use core::ops::Range;
+
+use sel4_bitfield_types::{get_bits, set_bits, UnsignedPrimInt};
+
+#[repr(C)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Debug)]
+pub struct Bitfield<T, const N: usize> {
+    arr: [T; N],
+}
+
+impl<T, const N: usize> Bitfield<T, N>
+where
+    T: UnsignedPrimInt,
+{
+    pub fn from_arr(arr: [T; N]) -> Self {
+        Self { arr }
+    }
+
+    pub fn into_arr(self) -> [T; N] {
+        self.arr
+    }
+
+    pub fn as_arr(&self) -> &[T; N] {
+        &self.arr
+    }
+
+    pub fn as_mut_arr(&mut self) -> &mut [T; N] {
+        &mut self.arr
+    }
+
+    pub fn zeroed() -> Self {
+        Self::from_arr([T::zero(); N])
+    }
+
+    pub fn get_bits(&self, range: Range<usize>) -> T {
+        get_bits(&self.arr, range)
+    }
+
+    pub fn set_bits(&mut self, range: Range<usize>, bits: T) {
+        set_bits(&mut self.arr, range, bits)
+    }
+}
diff --git a/crates/sel4/sys/src/ipc_buffer.rs b/crates/sel4/sys/src/ipc_buffer.rs
index 09cf12775..8ecf4e03e 100644
--- a/crates/sel4/sys/src/ipc_buffer.rs
+++ b/crates/sel4/sys/src/ipc_buffer.rs
@@ -2,7 +2,7 @@ use core::mem;
 use core::ops::Range;
 use core::slice;
 
-use sel4_bitfield_types::{get_bits_maybe_signed, set_bits_maybe_signed, PrimInt};
+use sel4_bitfield_types::{get_bits, set_bits, PrimInt};
 
 use crate::{seL4_CPtr, seL4_IPCBuffer, seL4_Word};
 
@@ -20,7 +20,7 @@ impl seL4_IPCBuffer {
         T: PrimInt,
         T::Unsigned: TryFrom<seL4_Word>,
     {
-        get_bits_maybe_signed(&self.msg, range)
+        T::cast_from_unsigned(get_bits(&self.msg, range))
     }
 
     pub(crate) fn set_mr_bits<T>(&mut self, range: Range<usize>, value: T)
@@ -28,7 +28,7 @@ impl seL4_IPCBuffer {
         T: PrimInt,
         T::Unsigned: TryInto<seL4_Word>,
     {
-        set_bits_maybe_signed(&mut self.msg, range, value)
+        set_bits(&mut self.msg, range, T::cast_to_unsigned(value))
     }
 
     pub(crate) fn msg_bytes_mut(&mut self) -> &'static mut [u8] {
diff --git a/crates/sel4/sys/src/syscalls/helpers/mod.rs b/crates/sel4/sys/src/syscalls/helpers/mod.rs
index 7b3fad444..f701f7596 100644
--- a/crates/sel4/sys/src/syscalls/helpers/mod.rs
+++ b/crates/sel4/sys/src/syscalls/helpers/mod.rs
@@ -1,4 +1,4 @@
-use sel4_bitfield_types::Bitfield;
+use crate::bf::types::Bitfield;
 
 use crate::{seL4_MessageInfo, seL4_Word};