diff --git a/rust/logos-blockchain-circuits-types/src/ffi/witness_input.rs b/rust/logos-blockchain-circuits-types/src/ffi/witness_input.rs
index d22bd18..431f959 100644
--- a/rust/logos-blockchain-circuits-types/src/ffi/witness_input.rs
+++ b/rust/logos-blockchain-circuits-types/src/ffi/witness_input.rs
@@ -1,6 +1,7 @@
 use std::ffi::c_char;
 use crate::ffi::ConstBytes;
 
+#[repr(C)]
 pub struct WitnessInput {
     pub dat: ConstBytes,
     pub inputs_json: *const c_char,
diff --git a/rust/logos-blockchain-circuits-types/src/native/bytes.rs b/rust/logos-blockchain-circuits-types/src/native/bytes.rs
index 0ce8d1c..f905a0b 100644
--- a/rust/logos-blockchain-circuits-types/src/native/bytes.rs
+++ b/rust/logos-blockchain-circuits-types/src/native/bytes.rs
@@ -4,11 +4,22 @@ pub struct Bytes(Vec<u8>);
 
 impl Bytes {
     #[must_use]
-    pub fn inner(&self) -> &Vec<u8> {
+    pub fn into_inner(self) -> Vec<u8> {
+        self.0
+    }
+    
+    #[must_use]
+    pub fn as_slice(&self) -> &[u8] {
         &self.0
     }
 }
 
+impl From<Vec<u8>> for Bytes {
+    fn from(value: Vec<u8>) -> Self {
+        Self(value)
+    }
+}
+
 impl From<ffi::Bytes> for Bytes {
     fn from(mut ffi_value: ffi::Bytes) -> Self {
         let raw = unsafe {
diff --git a/rust/logos-blockchain-circuits-types/src/native/witness_input.rs b/rust/logos-blockchain-circuits-types/src/native/witness_input.rs
index cce8ea0..562328a 100644
--- a/rust/logos-blockchain-circuits-types/src/native/witness_input.rs
+++ b/rust/logos-blockchain-circuits-types/src/native/witness_input.rs
@@ -1,4 +1,4 @@
-use std::ffi::{c_char, CString};
+use std::ffi::{c_char, CString, NulError};
 use crate::ffi;
 
 pub struct WitnessInput {
@@ -12,8 +12,7 @@ impl WitnessInput {
         Self { dat, inputs_json }
     }
 
-    #[must_use]
-    pub fn as_ffi(&'_ self) -> WitnessInputFfiGuard<'_> {
+    pub fn as_ffi(&'_ self) -> Result<WitnessInputFfiGuard<'_>, NulError> {
         WitnessInputFfiGuard::new(self)
     }
 }
@@ -28,15 +27,14 @@ pub struct WitnessInputFfiGuard<'a> {
 }
 
 impl<'a> WitnessInputFfiGuard<'a> {
-    #[must_use]
-    fn new(inner: &'a WitnessInput) -> Self {
+    fn new(inner: &'a WitnessInput) -> Result<Self, NulError> {
         let dat = ffi::ConstBytes { data: inner.dat.as_ptr(), size: inner.dat.len() };
-        let inputs_json = CString::new(inner.inputs_json.clone()).expect("CString::new failed").into_raw();
+        let inputs_json = CString::new(inner.inputs_json.clone())?.into_raw();
         let ffi = ffi::WitnessInput { dat, inputs_json };
-        Self {
+        Ok(Self {
             ffi,
             _lifetime: std::marker::PhantomData,
-        }
+        })
     }
 }
 
@@ -55,4 +53,3 @@ impl<'a> Drop for WitnessInputFfiGuard<'a> {
         }
     }
 }
-