diff --git a/src/group.cpp b/src/group.cpp
index 0f5a9e6..1cb1a1b 100644
--- a/src/group.cpp
+++ b/src/group.cpp
@@ -404,7 +404,11 @@ bool Group::IsForcedToMeshBySource() const {
 }
 
 bool Group::IsForcedToMesh() const {
-    return forceToMesh || IsForcedToMeshBySource();
+    return forceToMesh || IsTriangleMeshAssembly() || IsForcedToMeshBySource();
+}
+
+bool Group::IsTriangleMeshAssembly() const {
+    return type == Type::LINKED && linkFile.Extension() == "stl";
 }
 
 std::string Group::DescriptionString() {
diff --git a/src/importmesh.cpp b/src/importmesh.cpp
index 2115175..df9a65b 100644
--- a/src/importmesh.cpp
+++ b/src/importmesh.cpp
@@ -171,7 +171,6 @@ bool LinkStl(const Platform::Path &filename, EntityList *el, SMesh *m, SShell *s
         addUnique(verts, tr.b, normal);
         addUnique(verts, tr.c, normal);
     }
-    SK.GetGroup(SS.GW.activeGroup)->forceToMesh = true;
     dbp("%d verticies", verts.size());
 
     BBox box = {};
diff --git a/src/sketch.h b/src/sketch.h
index 6b58bb8..812375f 100644
--- a/src/sketch.h
+++ b/src/sketch.h
@@ -269,6 +269,7 @@ public:
     void Generate(EntityList *entity, ParamList *param);
     bool IsSolvedOkay();
     void TransformImportedBy(Vector t, Quaternion q);
+    bool IsTriangleMeshAssembly() const;
     bool IsForcedToMeshBySource() const;
     bool IsForcedToMesh() const;
     // When a request generates entities from entities, and the source
diff --git a/src/textscreens.cpp b/src/textscreens.cpp
index 628aff3..2255382 100644
--- a/src/textscreens.cpp
+++ b/src/textscreens.cpp
@@ -124,7 +124,7 @@ void TextWindow::ShowListOfGroups() {
             }
         }
         std::string suffix;
-        if(g->forceToMesh) {
+        if(g->forceToMesh || g->IsTriangleMeshAssembly()) {
             suffix = " (∆)";
         }
 
@@ -495,7 +495,7 @@ void TextWindow::ShowGroupInfo() {
         &TextWindow::ScreenChangeGroupOption,
         g->visible ? CHECK_TRUE : CHECK_FALSE);
 
-    if(!g->IsForcedToMeshBySource()) {
+    if(!g->IsForcedToMeshBySource() && !g->IsTriangleMeshAssembly()) {
         Printf(false, " %f%Lf%Fd%s  force NURBS surfaces to triangle mesh",
             &TextWindow::ScreenChangeGroupOption,
             g->forceToMesh ? CHECK_TRUE : CHECK_FALSE);