diff --git a/Cargo.lock b/Cargo.lock
index 9ec23e34e..afeac1e16 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -796,6 +796,7 @@ dependencies = [
  "fj-interop",
  "fj-kernel",
  "fj-math",
+ "thiserror",
 ]
 
 [[package]]
diff --git a/crates/fj-operations/Cargo.toml b/crates/fj-operations/Cargo.toml
index 5838307cb..78cad1ade 100644
--- a/crates/fj-operations/Cargo.toml
+++ b/crates/fj-operations/Cargo.toml
@@ -12,6 +12,9 @@ keywords = ["cad", "programmatic", "code-cad"]
 categories = ["encoding", "mathematics", "rendering"]
 
 
+[dependencies]
+thiserror = "1.0.31"
+
 [dependencies.fj]
 version = "0.6.0"
 path = "../fj"
diff --git a/crates/fj-operations/src/circle.rs b/crates/fj-operations/src/circle.rs
index ac643c5af..ac1c4dd3e 100644
--- a/crates/fj-operations/src/circle.rs
+++ b/crates/fj-operations/src/circle.rs
@@ -21,15 +21,12 @@ impl ToShape for fj::Circle {
         // to be added here.
 
         let edge = Edge::builder(&mut shape)
-            .build_circle(Scalar::from_f64(self.radius()))
-            .unwrap();
-        shape.insert(Cycle::new(vec![edge])).unwrap();
+            .build_circle(Scalar::from_f64(self.radius()))?;
+        shape.insert(Cycle::new(vec![edge]))?;
 
         let cycles = shape.cycles();
-        let surface = shape.insert(Surface::xy_plane()).unwrap();
-        shape
-            .insert(Face::new(surface, cycles, Vec::new(), self.color()))
-            .unwrap();
+        let surface = shape.insert(Surface::xy_plane())?;
+        shape.insert(Face::new(surface, cycles, Vec::new(), self.color()))?;
 
         Ok(shape)
     }
diff --git a/crates/fj-operations/src/difference_2d.rs b/crates/fj-operations/src/difference_2d.rs
index d10823a8d..f39df6da0 100644
--- a/crates/fj-operations/src/difference_2d.rs
+++ b/crates/fj-operations/src/difference_2d.rs
@@ -22,11 +22,12 @@ impl ToShape for fj::Difference2d {
         let mut exteriors = Vec::new();
         let mut interiors = Vec::new();
 
-        // Can be cleaned up, once `each_ref` is stable:
-        // https://doc.rust-lang.org/std/primitive.array.html#method.each_ref
+        // Can be cleaned up, once `each_ref` and `try_map` are stable:
+        // - https://doc.rust-lang.org/std/primitive.array.html#method.each_ref
+        // - https://doc.rust-lang.org/std/primitive.array.html#method.try_map
         let [a, b] = self.shapes();
-        let [a, b] =
-            [a, b].map(|shape| shape.to_shape(tolerance, debug_info).unwrap());
+        let [a, b] = [a, b].map(|shape| shape.to_shape(tolerance, debug_info));
+        let [a, b] = [a?, b?];
 
         if let Some(face) = a.faces().next() {
             // If there's at least one face to subtract from, we can proceed.
@@ -72,9 +73,12 @@ impl ToShape for fj::Difference2d {
                 }
             }
 
-            difference
-                .merge(Face::new(surface, exteriors, interiors, self.color()))
-                .unwrap();
+            difference.merge(Face::new(
+                surface,
+                exteriors,
+                interiors,
+                self.color(),
+            ))?;
         }
 
         Ok(difference)
diff --git a/crates/fj-operations/src/group.rs b/crates/fj-operations/src/group.rs
index 30f0aac23..99ffc75fd 100644
--- a/crates/fj-operations/src/group.rs
+++ b/crates/fj-operations/src/group.rs
@@ -18,8 +18,8 @@ impl ToShape for fj::Group {
         let a = self.a.to_shape(tolerance, debug_info)?;
         let b = self.b.to_shape(tolerance, debug_info)?;
 
-        copy_shape(a, &mut shape);
-        copy_shape(b, &mut shape);
+        shape.merge_shape(&a)?;
+        shape.merge_shape(&b)?;
 
         Ok(shape)
     }
@@ -31,9 +31,3 @@ impl ToShape for fj::Group {
         a.merged(&b)
     }
 }
-
-fn copy_shape(orig: Shape, target: &mut Shape) {
-    for face_orig in orig.faces() {
-        target.merge(face_orig.get()).unwrap();
-    }
-}
diff --git a/crates/fj-operations/src/shape_processor.rs b/crates/fj-operations/src/shape_processor.rs
index bb4855fe2..8d26eb010 100644
--- a/crates/fj-operations/src/shape_processor.rs
+++ b/crates/fj-operations/src/shape_processor.rs
@@ -2,7 +2,7 @@
 
 use fj_interop::{debug::DebugInfo, mesh::Mesh};
 use fj_kernel::{
-    algorithms::{triangulate, Tolerance},
+    algorithms::{triangulate, InvalidTolerance, Tolerance},
     shape::ValidationError,
 };
 use fj_math::{Aabb, Point, Scalar};
@@ -17,10 +17,7 @@ pub struct ShapeProcessor {
 
 impl ShapeProcessor {
     /// Process an [`fj::Shape`] into [`ProcessedShape`]
-    pub fn process(
-        &self,
-        shape: &fj::Shape,
-    ) -> Result<ProcessedShape, ValidationError> {
+    pub fn process(&self, shape: &fj::Shape) -> Result<ProcessedShape, Error> {
         let aabb = shape.bounding_volume();
 
         let tolerance = match self.tolerance {
@@ -36,7 +33,7 @@ impl ShapeProcessor {
                 }
 
                 let tolerance = min_extent / Scalar::from_f64(1000.);
-                Tolerance::from_scalar(tolerance).unwrap()
+                Tolerance::from_scalar(tolerance)?
             }
             Some(user_defined_tolerance) => user_defined_tolerance,
         };
@@ -69,3 +66,15 @@ pub struct ProcessedShape {
     /// The debug info generated while processing the shape
     pub debug_info: DebugInfo,
 }
+
+/// A shape processing error
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    /// Error converting to shape
+    #[error("Error converting to shape")]
+    ToShape(#[from] ValidationError),
+
+    /// Model has zero size
+    #[error("Model has an zero size")]
+    Extent(#[from] InvalidTolerance),
+}
diff --git a/crates/fj-operations/src/sketch.rs b/crates/fj-operations/src/sketch.rs
index 43cdc85b1..1100fc540 100644
--- a/crates/fj-operations/src/sketch.rs
+++ b/crates/fj-operations/src/sketch.rs
@@ -26,8 +26,7 @@ impl ToShape for fj::Sketch {
 
         Face::builder(surface, &mut shape)
             .with_exterior_polygon(points)
-            .build()
-            .unwrap();
+            .build()?;
 
         Ok(shape)
     }