diff --git a/src/containers/bitmap.rs b/src/containers/bitmap.rs
index b47cfbc..b6ed4f3 100644
--- a/src/containers/bitmap.rs
+++ b/src/containers/bitmap.rs
@@ -56,9 +56,8 @@ wrap_functions!(associate Bitmap;
     fn load(
         width: val usize,
         height: val usize,
-        data: val ByteSlice,
+        data: slice ByteSlice,
     ) -> move_ok *mut Bitmap {
-        let data = unsafe { data.as_slice() };
         Bitmap::load(width, height, data)
     };
 
@@ -97,7 +96,5 @@ wrap_methods!(Bitmap;
     /// Gets an unsafe reference to the data of the [Bitmap] instance.
     ///
     /// The returned memory is valid for the lifetime of the bitmap.
-    fn data_ref_mut(mut instance) -> val ByteSlice {
-        unsafe { ByteSlice::from_slice(instance.data_ref_mut()) }
-    };
+    fn data_ref_mut(mut instance) -> slice ByteSlice;
 );
diff --git a/src/containers/bitvec.rs b/src/containers/bitvec.rs
index 50a4eee..b16dd92 100644
--- a/src/containers/bitvec.rs
+++ b/src/containers/bitvec.rs
@@ -28,8 +28,7 @@ wrap_functions!(associate DisplayBitVec;
     /// Interpret the data as a series of bits and load then into a new [DisplayBitVec] instance.
     ///
     /// returns: [DisplayBitVec] instance containing data.
-    fn load(data: val ByteSlice) -> move NonNull<DisplayBitVec> {
-        let data = unsafe { data.as_slice() };
+    fn load(data: slice ByteSlice) -> move NonNull<DisplayBitVec> {
         DisplayBitVec::from_slice(data)
     };
 );
@@ -98,7 +97,5 @@ wrap_methods!(DisplayBitVec;
     /// Gets an unsafe reference to the data of the [DisplayBitVec] instance.
     ///
     /// The returned memory is valid for the lifetime of the bitvec.
-    fn as_raw_mut_slice(mut instance) -> val ByteSlice {
-        unsafe { ByteSlice::from_slice(instance.as_raw_mut_slice()) }
-    };
+    fn as_raw_mut_slice(mut instance) -> slice ByteSlice;
 );
diff --git a/src/containers/brightness_grid.rs b/src/containers/brightness_grid.rs
index f7cd099..19f6b7a 100644
--- a/src/containers/brightness_grid.rs
+++ b/src/containers/brightness_grid.rs
@@ -40,9 +40,8 @@ wrap_functions!(associate BrightnessGrid;
     fn load(
         width: val usize,
         height: val usize,
-        data: val ByteSlice,
+        data: slice ByteSlice,
     ) -> move_some *mut BrightnessGrid {
-        let data = unsafe { data.as_slice() };
         ByteGrid::load(width, height, data)
             .map(move |grid| grid.map(Brightness::saturating_from))
     };
@@ -64,13 +63,13 @@ wrap_methods!(BrightnessGrid;
     /// Gets an unsafe reference to the data of the instance.
     ///
     /// The returned memory is valid for the lifetime of the grid.
-    fn data_ref_mut(mut instance) -> val ByteSlice {
+    fn data_ref_mut(mut instance) -> slice ByteSlice {
         //noinspection RsAssertEqual
         const _: () = assert!(size_of::<Brightness>() == 1);
 
         let br_slice = instance.data_ref_mut();
         unsafe {
-            ByteSlice::from_slice(transmute::<&mut [Brightness], &mut [u8]>(br_slice))
+            transmute::<&mut [Brightness], &mut [u8]>(br_slice)
         }
     };
 );
diff --git a/src/containers/byte_slice.rs b/src/containers/byte_slice.rs
index d12cd88..81380e9 100644
--- a/src/containers/byte_slice.rs
+++ b/src/containers/byte_slice.rs
@@ -33,6 +33,7 @@ impl ByteSlice {
     };
 
     pub(crate) unsafe fn as_slice(&self) -> &[u8] {
+        assert!(!self.start.is_null());
         unsafe { std::slice::from_raw_parts(self.start, self.length) }
     }
 
diff --git a/src/containers/char_grid.rs b/src/containers/char_grid.rs
index a43f93d..98a2c5b 100644
--- a/src/containers/char_grid.rs
+++ b/src/containers/char_grid.rs
@@ -28,8 +28,7 @@ wrap_functions!(associate CharGrid;
     /// Loads a [CharGrid] with the specified dimensions from the provided data.
     ///
     /// returns: new CharGrid or NULL in case of an error
-    fn load(width: val usize, height: val usize, data: val ByteSlice) -> move_ok *mut CharGrid {
-        let data = unsafe { data.as_slice() };
+    fn load(width: val usize, height: val usize, data: slice ByteSlice) -> move_ok *mut CharGrid {
         CharGrid::load_utf8(width, height, data.to_vec())
     };
 );
diff --git a/src/containers/cp437_grid.rs b/src/containers/cp437_grid.rs
index e19ff72..62f0eb2 100644
--- a/src/containers/cp437_grid.rs
+++ b/src/containers/cp437_grid.rs
@@ -18,8 +18,7 @@ wrap_functions!(associate Cp437Grid;
     };
 
     /// Loads a [Cp437Grid] with the specified dimensions from the provided data.
-    fn load(width: val usize, height: val usize, data: val ByteSlice) -> move_some *mut Cp437Grid {
-        let data = unsafe { data.as_slice() };
+    fn load(width: val usize, height: val usize, data: slice ByteSlice) -> move_some *mut Cp437Grid {
         Cp437Grid::load(width, height, data)
     };
 );
@@ -40,7 +39,5 @@ wrap_methods!(Cp437Grid;
     /// Gets an unsafe reference to the data of the grid.
     ///
     /// The returned memory is valid for the lifetime of the instance.
-    fn data_ref_mut(mut instance) -> val ByteSlice {
-        unsafe { ByteSlice::from_slice(instance.data_ref_mut()) }
-    };
+    fn data_ref_mut(mut instance) -> slice ByteSlice;
 );
diff --git a/src/macros.rs b/src/macros.rs
index 086c901..79cd3af 100644
--- a/src/macros.rs
+++ b/src/macros.rs
@@ -169,6 +169,9 @@ macro_rules! apply_param_modifier {
     (ref, $param_name:ident) => {
         unsafe { $param_name.as_ref() }
     };
+    (slice, $param_name:ident) => {
+        unsafe { $param_name.as_slice() }
+    };
 }
 
 macro_rules! apply_return_modifier {
@@ -184,6 +187,9 @@ macro_rules! apply_return_modifier {
     (move_some, $result:ident) => {
         $crate::mem::heap_move_some($result)
     };
+    (slice, $result:ident) => {
+        unsafe { ByteSlice::from_slice($result) }
+    };
 }
 
 macro_rules! wrap_function {
diff --git a/src/packet.rs b/src/packet.rs
index abfa562..bec75e5 100644
--- a/src/packet.rs
+++ b/src/packet.rs
@@ -11,8 +11,7 @@ wrap_functions!(associate Packet;
     /// Tries to load a [Packet] from the passed array with the specified length.
     ///
     /// returns: NULL in case of an error, pointer to the allocated packet otherwise
-    fn try_load(data: val ByteSlice) -> move_ok *mut Packet {
-        let data = unsafe { data.as_slice() };
+    fn try_load(data: slice ByteSlice) -> move_ok *mut Packet {
         servicepoint::Packet::try_from(data)
     };