diff --git a/Cargo.lock b/Cargo.lock
index 3c24fa5ba..4da581ebf 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -904,7 +904,7 @@ checksum = "fc652a48c352aef3ea3aed32080501cf3ef6ed5da78602a020c991775b0aff04"
 [[package]]
 name = "cadkernel"
 version = "0.1.0"
-source = "git+https://github.com/HakanSeven12/cadkernel.git#962ffc3eda748a7d675ddc868be628c334e20a3b"
+source = "git+https://github.com/HakanSeven12/cadkernel.git#e3ff882a47c39104e04d07df8297ed02a4a657fe"
 dependencies = [
  "cavalier_contours",
 ]
diff --git a/src/scene/convert/acis_kernel.rs b/src/scene/convert/acis_kernel.rs
index fd1e13bc3..1b5c1630c 100644
--- a/src/scene/convert/acis_kernel.rs
+++ b/src/scene/convert/acis_kernel.rs
@@ -28,7 +28,18 @@ use crate::scene::model::mesh_model::MeshLodSet;
 const SAG: f64 = 0.05;
 
 /// What counts as the same point when the kernel reads a body over.
-const TOL: f64 = 1e-9;
+///
+/// A micrometre, in a drawing measured in metres. Not slackness: an edge is
+/// shared by two faces, and in a real file it cannot sit exactly on both,
+/// because the two surfaces were fitted separately and written to finite
+/// precision. Asked for exactness the kernel decides the edge is not on its
+/// own plane, declines to project it, and the face is dropped — twenty-six
+/// walls of one building went missing at a nanometre that no drawing means.
+///
+/// Loosening further buys almost nothing: a hundredth of this recovers one
+/// more face in sixty thousand, and past that the tolerance would start
+/// accepting geometry that really is wrong.
+const TOL: f64 = 1e-6;
 
 /// Tessellate an ACIS document by lifting it into the kernel.
 ///