diff --git a/ext/tests/secondary.rs b/ext/tests/secondary.rs
new file mode 100644
index 0000000000..50d3c253b5
--- /dev/null
+++ b/ext/tests/secondary.rs
@@ -0,0 +1,41 @@
+use std::sync::Arc;
+
+use ext::{
+    resolution_homomorphism::ResolutionHomomorphism, secondary::*, utils::construct_standard,
+};
+use sseq::coordinates::Bidegree;
+
+#[test]
+fn boundary_has_boundary() {
+    ext::utils::init_logging();
+
+    // Construct resolution of S_2 to stem 15
+    let resolution = Arc::new(construct_standard::<false, _, _>("S_2", None).unwrap());
+    resolution.compute_through_stem(Bidegree::n_s(15, 9));
+
+    // Lift to secondary resolution
+    let res_lift = Arc::new(SecondaryResolution::new(Arc::clone(&resolution)));
+    res_lift.extend_all();
+
+    // Construct lift of "h0". This could ready be any element, but we choose "h0" for simplicity.
+    let hom = ResolutionHomomorphism::from_class(
+        "h0".to_string(),
+        Arc::clone(&resolution),
+        Arc::clone(&resolution),
+        Bidegree::n_s(0, 1),
+        &[1],
+    );
+
+    // Extend only to stem 14. The class in (14, 3) is a boundary.
+    hom.extend_through_stem(Bidegree::n_s(14, 9));
+
+    // Lift to secondary homomorphism
+    let hom_lift = SecondaryResolutionHomomorphism::new(
+        Arc::clone(&res_lift),
+        Arc::clone(&res_lift),
+        Arc::new(hom),
+    );
+
+    // Crash
+    hom_lift.extend_all();
+}