diff --git a/src/srf/boolean.cpp b/src/srf/boolean.cpp
index 17e9d15c..296d6428 100644
--- a/src/srf/boolean.cpp
+++ b/src/srf/boolean.cpp
@@ -454,49 +454,48 @@ SSurface SSurface::MakeCopyTrimAgainst(SShell *parent,
     SEdgeList inter = {};
 
     SSurface *ss;
-    for(ss = agnst->surface.First(); ss; ss = agnst->surface.NextAfter(ss)) {
-        SCurve *sc;
-        for(sc = into->curve.First(); sc; sc = into->curve.NextAfter(sc)) {
-            if(sc->source != SCurve::Source::INTERSECTION) continue;
-            if(opA) {
-                if(sc->surfA != h || sc->surfB != ss->h) continue;
-            } else {
-                if(sc->surfB != h || sc->surfA != ss->h) continue;
-            }
+    SCurve *sc;
+    for(sc = into->curve.First(); sc; sc = into->curve.NextAfter(sc)) {
+        if(sc->source != SCurve::Source::INTERSECTION) continue;
+        if(opA) {
+            if(sc->surfA != h) continue;
+            ss = shb->surface.FindById(sc->surfB);
+        } else {
+            if(sc->surfB != h) continue;
+            ss = sha->surface.FindById(sc->surfA);
+        }
+        int i;
+        for(i = 1; i < sc->pts.n; i++) {
+            Vector a = sc->pts[i-1].p,
+                   b = sc->pts[i].p;
 
-            int i;
-            for(i = 1; i < sc->pts.n; i++) {
-                Vector a = sc->pts[i-1].p,
-                       b = sc->pts[i].p;
+            Point2d auv, buv;
+            ss->ClosestPointTo(a, &(auv.x), &(auv.y));
+            ss->ClosestPointTo(b, &(buv.x), &(buv.y));
 
-                Point2d auv, buv;
-                ss->ClosestPointTo(a, &(auv.x), &(auv.y));
-                ss->ClosestPointTo(b, &(buv.x), &(buv.y));
+            SBspUv::Class c = (ss->bsp) ? ss->bsp->ClassifyEdge(auv, buv, ss) : SBspUv::Class::OUTSIDE;
+            if(c != SBspUv::Class::OUTSIDE) {
+                Vector ta = Vector::From(0, 0, 0);
+                Vector tb = Vector::From(0, 0, 0);
+                ret.ClosestPointTo(a, &(ta.x), &(ta.y));
+                ret.ClosestPointTo(b, &(tb.x), &(tb.y));
 
-                SBspUv::Class c = (ss->bsp) ? ss->bsp->ClassifyEdge(auv, buv, ss) : SBspUv::Class::OUTSIDE;
-                if(c != SBspUv::Class::OUTSIDE) {
-                    Vector ta = Vector::From(0, 0, 0);
-                    Vector tb = Vector::From(0, 0, 0);
-                    ret.ClosestPointTo(a, &(ta.x), &(ta.y));
-                    ret.ClosestPointTo(b, &(tb.x), &(tb.y));
+                Vector tn = ret.NormalAt(ta.x, ta.y);
+                Vector sn = ss->NormalAt(auv.x, auv.y);
 
-                    Vector tn = ret.NormalAt(ta.x, ta.y);
-                    Vector sn = ss->NormalAt(auv.x, auv.y);
-
-                    // We are subtracting the portion of our surface that
-                    // lies in the shell, so the in-plane edge normal should
-                    // point opposite to the surface normal.
-                    bool bkwds = true;
-                    if((tn.Cross(b.Minus(a))).Dot(sn) < 0) bkwds = !bkwds;
-                    if((type == SSurface::CombineAs::DIFFERENCE && !opA) ||
-                       (type == SSurface::CombineAs::INTERSECTION)) { // Invert all newly created edges for intersection
-                        bkwds = !bkwds;
-                    }
-                    if(bkwds) {
-                        inter.AddEdge(tb, ta, sc->h.v, 1);
-                    } else {
-                        inter.AddEdge(ta, tb, sc->h.v, 0);
-                    }
+                // We are subtracting the portion of our surface that
+                // lies in the shell, so the in-plane edge normal should
+                // point opposite to the surface normal.
+                bool bkwds = true;
+                if((tn.Cross(b.Minus(a))).Dot(sn) < 0) bkwds = !bkwds;
+                if((type == SSurface::CombineAs::DIFFERENCE && !opA) ||
+                   (type == SSurface::CombineAs::INTERSECTION)) { // Invert all newly created edges for intersection
+                    bkwds = !bkwds;
+                }
+                if(bkwds) {
+                    inter.AddEdge(tb, ta, sc->h.v, 1);
+                } else {
+                    inter.AddEdge(ta, tb, sc->h.v, 0);
                 }
             }
         }