diff --git a/Cargo.lock b/Cargo.lock
index 0ba9197f87..77e57b2762 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4054,7 +4054,7 @@ dependencies = [
 [[package]]
 name = "solidcore"
 version = "0.0.1"
-source = "git+https://github.com/tangency-labs/solidcore?rev=b2450cbf941c83a1f9932d4cf629a6363840edb7#b2450cbf941c83a1f9932d4cf629a6363840edb7"
+source = "git+https://github.com/tangency-labs/solidcore?rev=937a63195fbf5a832c37271b1b3643e1c36bbec1#937a63195fbf5a832c37271b1b3643e1c36bbec1"
 dependencies = [
  "thiserror 2.0.21",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 2ff63500fe..d9865569e0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,7 +35,7 @@ solidcraft-3dx-client = { path = "crates/threedx-client" }
 # they reach parity (crates/smlib/src/route.rs). Pinned; move the rev on its own commit. For a
 # local checkout, add `[patch."https://github.com/tangency-labs/solidcore"] solidcore = { path =
 # "../solidcore/crates/solidcore" }` to a `.cargo/config.toml` outside the repository.
-solidcore = { git = "https://github.com/tangency-labs/solidcore", rev = "b2450cbf941c83a1f9932d4cf629a6363840edb7" }
+solidcore = { git = "https://github.com/tangency-labs/solidcore", rev = "937a63195fbf5a832c37271b1b3643e1c36bbec1" }
 
 # foundation
 thiserror = "2"
diff --git a/crates/smlib/src/core/sweep.rs b/crates/smlib/src/core/sweep.rs
index 7f8bcdf71b..40b2683f0f 100644
--- a/crates/smlib/src/core/sweep.rs
+++ b/crates/smlib/src/core/sweep.rs
@@ -1478,8 +1478,12 @@ pub(crate) fn project_curves(
         };
         let mut out = Vec::new();
         for c in &given {
-            let Some(root) = bspline(c)? else { return Ok(Err(Error::Argument)) };
-            let made = match create_parallel_projection_curves(k, b, &root, dir, &opts) {
+            // curve->GetRootCurve(): a line, an arc and a B-spline are their own root, and
+            // go in as themselves
+            if !matches!(c.kind(), CurveKind::BSpline(_) | CurveKind::Line(_) | CurveKind::Ellipse(_)) {
+                return Ok(Err(Error::Argument));
+            }
+            let made = match create_parallel_projection_curves(k, b, c, dir, &opts) {
                 Ok(m) => m.curves_3d.unwrap_or_default(),
                 Err(e) => return Ok(Err(status(e))),
             };