diff --git a/crates/fj-kernel/src/algorithms/intersect/curve_edge.rs b/crates/fj-kernel/src/algorithms/intersect/curve_edge.rs
index 1b6d14a8b..ac53e7fff 100644
--- a/crates/fj-kernel/src/algorithms/intersect/curve_edge.rs
+++ b/crates/fj-kernel/src/algorithms/intersect/curve_edge.rs
@@ -87,12 +87,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?;
         let half_edge = HalfEdge::partial()
             .update_as_line_segment_from_points(surface, [[1., -1.], [1., 1.]])
             .build(&objects)?;
@@ -113,12 +113,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?;
         let half_edge = HalfEdge::partial()
             .update_as_line_segment_from_points(
                 surface,
@@ -142,12 +142,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?;
         let half_edge = HalfEdge::partial()
             .update_as_line_segment_from_points(
                 surface,
@@ -166,12 +166,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?;
         let half_edge = HalfEdge::partial()
             .update_as_line_segment_from_points(surface, [[-1., 0.], [1., 0.]])
             .build(&objects)?;
diff --git a/crates/fj-kernel/src/algorithms/intersect/surface_surface.rs b/crates/fj-kernel/src/algorithms/intersect/surface_surface.rs
index ebc7c2d16..43ed585d6 100644
--- a/crates/fj-kernel/src/algorithms/intersect/surface_surface.rs
+++ b/crates/fj-kernel/src/algorithms/intersect/surface_surface.rs
@@ -119,20 +119,18 @@ mod tests {
             None,
         );
 
-        let expected_xy = PartialCurve {
+        let mut expected_xy = PartialCurve {
             surface: Some(xy.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?
-        .insert(&objects)?;
-        let expected_xz = PartialCurve {
+        };
+        expected_xy.update_as_u_axis();
+        let expected_xy = expected_xy.build(&objects)?.insert(&objects)?;
+        let mut expected_xz = PartialCurve {
             surface: Some(xz.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?
-        .insert(&objects)?;
+        };
+        expected_xz.update_as_u_axis();
+        let expected_xz = expected_xz.build(&objects)?.insert(&objects)?;
 
         assert_eq!(
             SurfaceSurfaceIntersection::compute([xy, xz], &objects)?,
diff --git a/crates/fj-kernel/src/algorithms/sweep/vertex.rs b/crates/fj-kernel/src/algorithms/sweep/vertex.rs
index 750a0c338..69c557727 100644
--- a/crates/fj-kernel/src/algorithms/sweep/vertex.rs
+++ b/crates/fj-kernel/src/algorithms/sweep/vertex.rs
@@ -179,13 +179,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xz_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?
-        .insert(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?.insert(&objects)?;
         let vertex = Vertex::partial()
             .with_position(Some([0.]))
             .with_curve(curve)
diff --git a/crates/fj-kernel/src/builder/curve.rs b/crates/fj-kernel/src/builder/curve.rs
index 2e6b15827..1380bfff8 100644
--- a/crates/fj-kernel/src/builder/curve.rs
+++ b/crates/fj-kernel/src/builder/curve.rs
@@ -5,7 +5,7 @@ use crate::{partial::PartialCurve, path::SurfacePath};
 /// Builder API for [`PartialCurve`]
 pub trait CurveBuilder {
     /// Update partial curve to represent the u-axis
-    fn update_as_u_axis(self) -> Self;
+    fn update_as_u_axis(&mut self) -> &mut Self;
 
     /// Update partial curve to represent the v-axis
     fn update_as_v_axis(&mut self) -> &mut Self;
@@ -24,12 +24,11 @@ pub trait CurveBuilder {
 }
 
 impl CurveBuilder for PartialCurve {
-    fn update_as_u_axis(mut self) -> Self {
+    fn update_as_u_axis(&mut self) -> &mut Self {
         let a = Point::origin();
         let b = a + Vector::unit_u();
 
-        self.update_as_line_from_points([a, b]);
-        self
+        self.update_as_line_from_points([a, b])
     }
 
     fn update_as_v_axis(&mut self) -> &mut Self {
diff --git a/crates/fj-kernel/src/iter.rs b/crates/fj-kernel/src/iter.rs
index b3bbc65ac..f68e0c1c6 100644
--- a/crates/fj-kernel/src/iter.rs
+++ b/crates/fj-kernel/src/iter.rs
@@ -376,13 +376,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let object = PartialCurve {
+        let mut object = PartialCurve {
             surface: Some(surface),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?
-        .insert(&objects)?;
+        };
+        object.update_as_u_axis();
+        let object = object.build(&objects)?.insert(&objects)?;
 
         assert_eq!(1, object.curve_iter().count());
         assert_eq!(0, object.cycle_iter().count());
@@ -618,13 +617,12 @@ mod tests {
         let objects = Objects::new();
 
         let surface = objects.surfaces.xy_plane();
-        let curve = PartialCurve {
+        let mut curve = PartialCurve {
             surface: Some(surface.clone()),
             ..Default::default()
-        }
-        .update_as_u_axis()
-        .build(&objects)?
-        .insert(&objects)?;
+        };
+        curve.update_as_u_axis();
+        let curve = curve.build(&objects)?.insert(&objects)?;
         let global_vertex = objects
             .global_vertices
             .insert(GlobalVertex::from_position([0., 0., 0.]))?;
diff --git a/crates/fj-kernel/src/validate/vertex.rs b/crates/fj-kernel/src/validate/vertex.rs
index 2d04eab55..6b76257b1 100644
--- a/crates/fj-kernel/src/validate/vertex.rs
+++ b/crates/fj-kernel/src/validate/vertex.rs
@@ -190,15 +190,15 @@ mod tests {
     fn vertex_surface_mismatch() -> anyhow::Result<()> {
         let objects = Objects::new();
 
+        let mut curve = PartialCurve {
+            surface: Some(objects.surfaces.xy_plane()),
+            ..Default::default()
+        };
+        curve.update_as_u_axis();
+
         let valid = Vertex::partial()
             .with_position(Some([0.]))
-            .with_curve(
-                PartialCurve {
-                    surface: Some(objects.surfaces.xy_plane()),
-                    ..Default::default()
-                }
-                .update_as_u_axis(),
-            )
+            .with_curve(curve)
             .build(&objects)?;
         let invalid = Vertex::new(
             valid.position(),
@@ -221,16 +221,18 @@ mod tests {
     fn vertex_position_mismatch() -> anyhow::Result<()> {
         let objects = Objects::new();
 
-        let valid = Vertex::partial()
-            .with_position(Some([0.]))
-            .with_curve(
-                PartialCurve {
-                    surface: Some(objects.surfaces.xy_plane()),
-                    ..Default::default()
-                }
-                .update_as_u_axis(),
-            )
-            .build(&objects)?;
+        let valid = {
+            let mut curve = PartialCurve {
+                surface: Some(objects.surfaces.xy_plane()),
+                ..Default::default()
+            };
+            curve.update_as_u_axis();
+
+            Vertex::partial()
+                .with_position(Some([0.]))
+                .with_curve(curve)
+                .build(&objects)?
+        };
         let invalid = Vertex::new(
             valid.position(),
             valid.curve().clone(),