diff --git a/Cargo.lock b/Cargo.lock
index 0c89d6f..0fe1b9e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -84,8 +84,6 @@ dependencies = [
 [[package]]
 name = "clipper2c-sys"
 version = "0.1.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e2995248c63ec82bf22c921cfd26fe407a4402b7039e045d286f7470cd83fe9e"
 dependencies = [
  "cc",
  "libc",
diff --git a/Cargo.toml b/Cargo.toml
index 946a566..d73aab5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,6 +15,7 @@ categories = ["algorithms"]
 default = ["doc-images"]
 doc-images = []
 serde = ["dep:serde", "clipper2c-sys/serde"]
+usingz = ["clipper2c-sys/usingz"]
 
 [dependencies]
 libc = "0.2"
@@ -31,3 +32,6 @@ serde_json = "1"
 # docs.rs uses a nightly compiler, so by instructing it to use our `doc-images` feature we
 # ensure that it will render any images that we may have in inner attribute documentation.
 features = ["doc-images"]
+
+[patch.crates-io]
+clipper2c-sys = { path = "../clipper2c-sys" }
diff --git a/src/clipper.rs b/src/clipper.rs
index d6f317b..f52ca13 100644
--- a/src/clipper.rs
+++ b/src/clipper.rs
@@ -2,11 +2,12 @@ use std::marker::PhantomData;
 
 use clipper2c_sys::{
     clipper_clipper64, clipper_clipper64_add_clip, clipper_clipper64_add_open_subject,
-    clipper_clipper64_add_subject, clipper_clipper64_execute, clipper_clipper64_size,
-    clipper_delete_clipper64, clipper_delete_paths64, ClipperClipper64,
+    clipper_clipper64_add_subject, clipper_clipper64_execute, clipper_clipper64_set_z_callback,
+    clipper_clipper64_size, clipper_delete_clipper64, clipper_delete_paths64, ClipperClipper64,
+    ClipperPoint64,
 };
 
-use crate::{malloc, Centi, ClipType, FillRule, Paths, PointScaler};
+use crate::{malloc, Centi, ClipType, FillRule, Paths, Point, PointScaler};
 
 /// The state of the Clipper struct.
 pub trait ClipperState {}
@@ -27,12 +28,29 @@ pub struct WithClips {}
 impl ClipperState for WithClips {}
 
 /// The Clipper struct used as a builder for applying boolean operations to paths.
-#[derive(Debug)]
 pub struct Clipper<S: ClipperState = NoSubjects, P: PointScaler = Centi> {
     ptr: *mut ClipperClipper64,
     keep_ptr_on_drop: bool,
     _marker: PhantomData<P>,
     _state: S,
+
+    /// We only hold on to this in order to avoid leaking memory when Clipper is dropped
+    #[cfg(feature = "usingz")]
+    raw_z_callback: Option<*mut libc::c_void>,
+}
+
+impl<S: ClipperState + std::fmt::Debug, P: PointScaler + std::fmt::Debug> std::fmt::Debug
+    for Clipper<S, P>
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Clipper")
+            .field("ptr", &self.ptr)
+            .field("keep_ptr_on_drop", &self.keep_ptr_on_drop)
+            .field("_marker", &self._marker)
+            .field("_state", &self._state)
+            .field("raw_z_callback", &self.raw_z_callback.is_some())
+            .finish()
+    }
 }
 
 impl<P: PointScaler> Clipper<NoSubjects, P> {
@@ -48,6 +66,9 @@ impl<P: PointScaler> Clipper<NoSubjects, P> {
             keep_ptr_on_drop: false,
             _marker: PhantomData,
             _state: NoSubjects {},
+
+            #[cfg(feature = "usingz")]
+            raw_z_callback: None,
         }
     }
 }
@@ -72,6 +93,9 @@ impl<P: PointScaler> Clipper<NoSubjects, P> {
             keep_ptr_on_drop: false,
             _marker: PhantomData,
             _state: WithSubjects {},
+
+            #[cfg(feature = "usingz")]
+            raw_z_callback: None,
         };
 
         drop(self);
@@ -98,12 +122,84 @@ impl<P: PointScaler> Clipper<NoSubjects, P> {
             keep_ptr_on_drop: false,
             _marker: PhantomData,
             _state: WithSubjects {},
+
+            #[cfg(feature = "usingz")]
+            raw_z_callback: None,
         };
 
         drop(self);
 
         clipper.add_open_subject(subject)
     }
+
+    #[cfg(feature = "usingz")]
+    /// Allows specifying a callback that will be called each time a new vertex
+    /// is created by Clipper, in order to set user data on such points. New
+    /// points are created at the intersections between two edges, and the
+    /// callback will be called with the four neighboring points from those two
+    /// edges. The last argument is the new point itself.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use clipper2::*;
+    ///
+    /// let mut clipper = Clipper::<NoSubjects, Centi>::new();
+    /// clipper.set_z_callback(|_: Point<_>, _: Point<_>, _: Point<_>, _: Point<_>, p: &mut Point<_>| {
+    ///     p.set_z(1);
+    /// });
+    /// ```
+    pub fn set_z_callback(
+        &mut self,
+        callback: impl Fn(Point<P>, Point<P>, Point<P>, Point<P>, &mut Point<P>),
+    ) {
+        // The closure will be represented by a trait object behind a fat
+        // pointer. Since fat pointers are larger than thin pointers, they
+        // cannot be passed through a thin-pointer c_void type. We must
+        // therefore wrap the fat pointer in another box, leading to this double
+        // indirection.
+        let cb: Box<Box<dyn Fn(Point<P>, Point<P>, Point<P>, Point<P>, &mut Point<P>)>> =
+            Box::new(Box::new(callback));
+        let raw_cb = Box::into_raw(cb) as *mut _;
+
+        // It there is an old callback stored, drop it before replacing it
+        if let Some(old_raw_cb) = self.raw_z_callback {
+            drop(unsafe { Box::from_raw(old_raw_cb as *mut _) });
+        }
+        self.raw_z_callback = Some(raw_cb);
+
+        unsafe {
+            clipper_clipper64_set_z_callback(self.ptr, raw_cb, Some(handle_set_z_callback::<P>));
+        }
+    }
+}
+
+extern "C" fn handle_set_z_callback<P: PointScaler>(
+    user_data: *mut ::std::os::raw::c_void,
+    e1bot: *const ClipperPoint64,
+    e1top: *const ClipperPoint64,
+    e2bot: *const ClipperPoint64,
+    e2top: *const ClipperPoint64,
+    pt: *mut ClipperPoint64,
+) {
+    // SAFETY: user_data was set in set_z_callback, and is valid for as long as
+    // the Clipper2 instance exists.
+    let callback: &mut &mut dyn Fn(Point<P>, Point<P>, Point<P>, Point<P>, &mut Point<P>) =
+        unsafe { std::mem::transmute(user_data) };
+
+    // SAFETY: Clipper2 should produce valid pointers
+    let mut new_point = unsafe { Point::<P>::from(*pt) };
+    let e1bot = unsafe { Point::<P>::from(*e1bot) };
+    let e1top = unsafe { Point::<P>::from(*e1top) };
+    let e2bot = unsafe { Point::<P>::from(*e2bot) };
+    let e2top = unsafe { Point::<P>::from(*e2top) };
+
+    callback(e1bot, e1top, e2bot, e2top, &mut new_point);
+
+    // SAFETY: pt is a valid pointer and new_point is not null
+    unsafe {
+        *pt = *new_point.as_clipperpoint64();
+    }
 }
 
 impl<P: PointScaler> Clipper<WithSubjects, P> {
@@ -171,6 +267,9 @@ impl<P: PointScaler> Clipper<WithSubjects, P> {
             keep_ptr_on_drop: false,
             _marker: PhantomData,
             _state: WithClips {},
+
+            #[cfg(feature = "usingz")]
+            raw_z_callback: None,
         };
 
         drop(self);
@@ -321,6 +420,13 @@ impl<S: ClipperState, P: PointScaler> Drop for Clipper<S, P> {
     fn drop(&mut self) {
         if !self.keep_ptr_on_drop {
             unsafe { clipper_delete_clipper64(self.ptr) }
+
+            #[cfg(feature = "usingz")]
+            {
+                if let Some(raw_cb) = self.raw_z_callback {
+                    drop(unsafe { Box::from_raw(raw_cb as *mut _) });
+                }
+            }
         }
     }
 }
@@ -332,3 +438,47 @@ pub enum ClipperError {
     #[error("Failed boolean operation")]
     FailedBooleanOperation,
 }
+
+#[cfg(test)]
+mod test {
+    use std::{cell::Cell, rc::Rc};
+
+    use super::*;
+
+    #[cfg(feature = "usingz")]
+    #[test]
+    fn test_set_z_callback() {
+        let mut clipper = Clipper::<NoSubjects, Centi>::new();
+        let success = Rc::new(Cell::new(false));
+        {
+            let success = success.clone();
+            clipper.set_z_callback(
+                move |_e1bot: Point<_>,
+                      _e1top: Point<_>,
+                      _e2bot: Point<_>,
+                      _e2top: Point<_>,
+                      p: &mut Point<_>| {
+                    p.set_z(1);
+                    success.set(true);
+                },
+            );
+        }
+        let e1: Paths = vec![(0.0, 0.0), (2.0, 2.0), (0.0, 2.0)].into();
+        let e2: Paths = vec![(1.0, 0.0), (2.0, 0.0), (1.0, 2.0)].into();
+        let paths = clipper
+            .add_subject(e1)
+            .add_clip(e2)
+            .union(FillRule::default())
+            .unwrap();
+
+        assert_eq!(success.get(), true);
+
+        let n_intersecting = paths
+            .iter()
+            .flatten()
+            .into_iter()
+            .filter(|v| v.z() == 1)
+            .count();
+        assert_eq!(n_intersecting, 3);
+    }
+}
diff --git a/src/path.rs b/src/path.rs
index c659d0e..13aa847 100644
--- a/src/path.rs
+++ b/src/path.rs
@@ -322,6 +322,7 @@ impl<P: PointScaler> Path<P> {
                 .map(|point: Point<P>| ClipperPoint64 {
                     x: point.x_scaled(),
                     y: point.y_scaled(),
+                    ..Default::default()
                 })
                 .collect::<Vec<_>>()
                 .as_mut_ptr(),
diff --git a/src/point.rs b/src/point.rs
index 747b647..266d218 100644
--- a/src/point.rs
+++ b/src/point.rs
@@ -97,9 +97,15 @@ pub struct Point<P: PointScaler = Centi>(
 );
 
 impl<P: PointScaler> Point<P> {
+    #[cfg(not(feature = "usingz"))]
     /// The zero point.
     pub const ZERO: Self = Self(ClipperPoint64 { x: 0, y: 0 }, PhantomData);
 
+    #[cfg(feature = "usingz")]
+    /// The zero point.
+    pub const ZERO: Self = Self(ClipperPoint64 { x: 0, y: 0, z: 0 }, PhantomData);
+
+    #[cfg(not(feature = "usingz"))]
     /// The minimum value for a point.
     pub const MIN: Self = Self(
         ClipperPoint64 {
@@ -109,6 +115,18 @@ impl<P: PointScaler> Point<P> {
         PhantomData,
     );
 
+    #[cfg(feature = "usingz")]
+    /// The minimum value for a point.
+    pub const MIN: Self = Self(
+        ClipperPoint64 {
+            x: i64::MIN,
+            y: i64::MIN,
+            z: 0,
+        },
+        PhantomData,
+    );
+
+    #[cfg(not(feature = "usingz"))]
     /// The maximum value for a point.
     pub const MAX: Self = Self(
         ClipperPoint64 {
@@ -118,12 +136,24 @@ impl<P: PointScaler> Point<P> {
         PhantomData,
     );
 
+    #[cfg(feature = "usingz")]
+    /// The maximum value for a point.
+    pub const MAX: Self = Self(
+        ClipperPoint64 {
+            x: i64::MAX,
+            y: i64::MAX,
+            z: 0,
+        },
+        PhantomData,
+    );
+
     /// Create a new point.
     pub fn new(x: f64, y: f64) -> Self {
         Self(
             ClipperPoint64 {
                 x: P::scale(x) as i64,
                 y: P::scale(y) as i64,
+                ..Default::default()
             },
             PhantomData,
         )
@@ -132,7 +162,14 @@ impl<P: PointScaler> Point<P> {
     /// Create a new point from scaled values, this means that point is
     /// constructed as is without applying the scaling multiplier.
     pub fn from_scaled(x: i64, y: i64) -> Self {
-        Self(ClipperPoint64 { x, y }, PhantomData)
+        Self(
+            ClipperPoint64 {
+                x,
+                y,
+                ..Default::default()
+            },
+            PhantomData,
+        )
     }
 
     /// Returns the x coordinate of the point.
@@ -158,6 +195,18 @@ impl<P: PointScaler> Point<P> {
     pub(crate) fn as_clipperpoint64(&self) -> *const ClipperPoint64 {
         &self.0
     }
+
+    #[cfg(feature = "usingz")]
+    /// Returns the user data of the point.
+    pub fn z(&self) -> i64 {
+        self.0.z
+    }
+
+    #[cfg(feature = "usingz")]
+    /// Sets the user data of the point.
+    pub fn set_z(&mut self, z: i64) {
+        self.0.z = z;
+    }
 }
 
 impl<P: PointScaler> Default for Point<P> {