diff --git a/crates/kernel/src/iges_in.rs b/crates/kernel/src/iges_in.rs
index cbb6716ecc..d9f1f7f874 100644
--- a/crates/kernel/src/iges_in.rs
+++ b/crates/kernel/src/iges_in.rs
@@ -660,6 +660,8 @@ impl<'a> Tr<'a> {
         self.nurbs_curve_in(seq, x, self.f.unit)
     }
     fn nurbs_curve_in(&self, seq: i64, x: &Xf, unit: f64) -> R<Nurbs> {
+        /// Knot spans shorter than this are moved onto (0, 1).
+        const MIN_KNOT_SPAN: f64 = 1e-4;
         let k = self.i(seq, 1)?;
         let m = self.i(seq, 2)?;
         if !(0..=MAX_LIST as i64).contains(&k) || !(1..=32).contains(&m) || m > k.max(1) + 1 {
@@ -685,11 +687,21 @@ impl<'a> Tr<'a> {
         if knots.windows(2).any(|w| w[1] < w[0]) {
             return Err(format!("entity {seq}: knots out of order"));
         }
-        let nb = Nurbs { deg: m, knots, pts };
+        let mut nb = Nurbs { deg: m, knots, pts };
         let (a, b) = nb.range();
         if !(b > a) {
             return Err(format!("entity {seq}: empty parameter range"));
         }
+        // Some exporters write a curve over a knot span of 1e-7 or less. The STEP side reads a
+        // span that small as a single value and refused the curve, losing the faces it bounds.
+        // Moving and scaling the knots onto (0, 1) leaves the curve's shape as it is; nothing
+        // else refers to its parameters.
+        if b - a < MIN_KNOT_SPAN {
+            let scale = 1.0 / (b - a);
+            for k in &mut nb.knots {
+                *k = (*k - a) * scale;
+            }
+        }
         Ok(nb)
     }
 
diff --git a/crates/kernel/src/iges_in/tests.rs b/crates/kernel/src/iges_in/tests.rs
index c10950c364..5aa7738a27 100644
--- a/crates/kernel/src/iges_in/tests.rs
+++ b/crates/kernel/src/iges_in/tests.rs
@@ -342,3 +342,42 @@ fn a_hole_whose_first_trim_piece_is_reversed_stays_a_hole() {
     let m = measure(&imp.bodies[0].body).unwrap();
     assert!(rel(m.area, 84.0) < 1e-6, "area {}", m.area);
 }
+
+/// The box of `trimmed_surfaces_sew_into_a_solid` with one edge written as a B-spline (126)
+/// over a knot span of 1e-7 or less, as some exporters write short curves: the STEP side read
+/// that span as a single value and refused the curve, and both faces it bounds were lost.
+#[test]
+fn a_curve_over_a_tiny_knot_span_still_bounds_its_faces() {
+    let c =
+        |i: usize| -> [f64; 3] { [if i & 1 != 0 { 10.0 } else { 0.0 }, if i & 2 != 0 { 20.0 } else { 0.0 }, if i & 4 != 0 { 30.0 } else { 0.0 }] };
+    let quads = [[0, 2, 3, 1], [4, 5, 7, 6], [0, 1, 5, 4], [2, 6, 7, 3], [0, 4, 6, 2], [1, 3, 7, 5]];
+    let fmt = |p: [f64; 3]| format!("{:?},{:?},{:?}", p[0], p[1], p[2]);
+    for span in [1e-7f64, 1e-9, 1e-13] {
+        let mut ents: Vec<(i64, i64, String)> = Vec::new();
+        for (fi, q) in quads.iter().enumerate() {
+            let (a, b, cc, d) = (c(q[0]), c(q[1]), c(q[2]), c(q[3]));
+            let surf = format!("1,1,1,1,0,0,1,0,0,0.,0.,1.,1.,0.,0.,1.,1.,1.,1.,1.,1.,{},{},{},{},0.,1.,0.,1.", fmt(a), fmt(b), fmt(d), fmt(cc));
+            ents.push((128, 0, surf));
+            let s_de = 2 * ents.len() - 1;
+            let mut lines = Vec::new();
+            for (k, (p0, p1)) in [(a, b), (b, cc), (cc, d), (d, a)].into_iter().enumerate() {
+                if fi == 0 && k == 0 {
+                    ents.push((126, 0, format!("1,1,0,0,1,0,0.,0.,{span:E},{span:E},1.,1.,{},{},0.,{span:E},0.,0.,1.", fmt(p0), fmt(p1))));
+                } else {
+                    ents.push((110, 0, format!("{},{}", fmt(p0), fmt(p1))));
+                }
+                lines.push(2 * ents.len() - 1);
+            }
+            ents.push((102, 0, format!("4,{}", lines.iter().map(|x| x.to_string()).collect::<Vec<_>>().join(","))));
+            let comp = 2 * ents.len() - 1;
+            ents.push((142, 0, format!("0,{s_de},0,{comp},2")));
+            let cos = 2 * ents.len() - 1;
+            ents.push((144, 0, format!("{s_de},1,0,{cos}")));
+        }
+        let imp = iges_import(&iges_file(&ents)).unwrap();
+        assert!(imp.warnings.is_empty(), "span {span}: {:?}", imp.warnings);
+        assert!(imp.bodies[0].closed, "span {span}");
+        let m = measure(&imp.bodies[0].body).unwrap();
+        assert!(rel(m.volume, 6000.0) < 1e-6 && rel(m.area, 2200.0) < 1e-6, "span {span}: {} {}", m.volume, m.area);
+    }
+}