diff --git a/assets/locales/pending/rigid-group-selection.json b/assets/locales/pending/rigid-group-selection.json
new file mode 100644
index 0000000000..28ede4387b
--- /dev/null
+++ b/assets/locales/pending/rigid-group-selection.json
@@ -0,0 +1,14 @@
+{
+  "en": {
+    "joint.rigid_group_one_component": "These {count} bodies are all in one component (or in the design itself): use {command} first.",
+    "joint.rigid_group_select_components": "Select two or more components."
+  },
+  "ja": {
+    "joint.rigid_group_one_component": "これらの {count} 個のボディは、すべて 1 つのコンポーネント内（またはデザイン自体）にあります。先に「{command}」を使用してください。",
+    "joint.rigid_group_select_components": "2 つ以上のコンポーネントを選択してください。"
+  },
+  "zh": {
+    "joint.rigid_group_one_component": "这 {count} 个实体都位于同一组件中（或直接位于设计中）：请先使用“{command}”。",
+    "joint.rigid_group_select_components": "请选择两个或更多组件。"
+  }
+}
diff --git a/crates/ui-egui/src/dialogs_assembly.rs b/crates/ui-egui/src/dialogs_assembly.rs
index 1f18e6da61..b1b4272b85 100644
--- a/crates/ui-egui/src/dialogs_assembly.rs
+++ b/crates/ui-egui/src/dialogs_assembly.rs
@@ -973,9 +973,16 @@ pub fn commands(app: &SolveApp, k: &Asm, inputs: &[SelInput]) -> Result<Vec<(Str
             cmd("joint.origin", p)
         }
         Asm::RigidGroup => {
-            let occs = occurrences(s, sel_items(inputs, 0));
+            let items = sel_items(inputs, 0);
+            let occs = occurrences(s, items);
             if occs.len() < 2 {
-                return Err("select two or more components".into());
+                if occs.len() == 1 && items.len() > 1 && items.iter().all(|x| matches!(x, Sel::Body { .. })) {
+                    return Err(crate::i18n::format(
+                        "joint.rigid_group_one_component",
+                        &[("count", &items.len().to_string()), ("command", crate::i18n::tr("cmd.component_from_bodies"))],
+                    ));
+                }
+                return Err(crate::i18n::tr("joint.rigid_group_select_components").into());
             }
             cmd("joint.rigid_group", json!({ "occurrences": occs }))
         }
diff --git a/crates/ui-egui/src/dialogs_assembly_tests.rs b/crates/ui-egui/src/dialogs_assembly_tests.rs
index f8c39683c5..67eef3934f 100644
--- a/crates/ui-egui/src/dialogs_assembly_tests.rs
+++ b/crates/ui-egui/src/dialogs_assembly_tests.rs
@@ -455,6 +455,45 @@ fn picks_on_one_component_say_why_and_offer_components() {
     assert!(text_at(&out, &why).is_none(), "nothing left to say");
 }
 
+#[test]
+fn rigid_group_bodies_in_one_component_explain_how_to_separate_them() {
+    for component in [None, Some("Part")] {
+        let mut s = Session::default();
+        if let Some(name) = component {
+            s.execute("component.create", &json!({"name": name})).unwrap();
+        }
+        for x in [0, 30, 60, 90, 120] {
+            s.execute("solid.box", &json!({"length": 10, "width": 10, "height": 10, "corner": [x, 0, 0]})).unwrap();
+        }
+        let mut app = SolveApp::new(s, Services::default());
+        app.session.selection = (1..=5).map(|i| Sel::Body { name: format!("Body{i}") }).collect();
+        app.start("joint.rigid_group");
+        let d = app.dialog.take().unwrap();
+        assert_eq!(
+            apply_commands(&app, &d).unwrap_err(),
+            "These 5 bodies are all in one component (or in the design itself): use Create Components from Bodies first."
+        );
+        app.run("component.from_bodies", json!({"bodies": ["Body1", "Body2", "Body3", "Body4", "Body5"]})).unwrap();
+        assert_eq!(apply_commands(&app, &d).unwrap()[0].1["occurrences"].as_array().unwrap().len(), 5);
+    }
+}
+
+#[test]
+fn rigid_group_preserves_two_instances_of_one_component() {
+    let mut s = Session::default();
+    let first = s.execute("component.create", &json!({"name": "Part"})).unwrap()["occurrence"].as_u64().unwrap();
+    s.execute("solid.box", &json!({"length": 10, "width": 10, "height": 10})).unwrap();
+    let second = s.execute("occurrence.copy", &json!({"occurrence": first, "translate": [30, 0, 0]})).unwrap()["occurrence"].as_u64().unwrap();
+    s.selection = [first, second].into_iter().map(|id| Sel::Body { name: s.occurrence_bodies(&[id], false).unwrap()[0].clone() }).collect();
+    let mut app = SolveApp::new(s, Services::default());
+    app.start("joint.rigid_group");
+    let d = app.dialog.take().unwrap();
+    let commands = apply_commands(&app, &d).unwrap();
+    assert_eq!(commands, vec![("joint.rigid_group".into(), json!({"occurrences": [first, second]}))]);
+    crate::dialogs::run_dialog(&mut app, &d).unwrap();
+    assert_eq!(app.session.doc.assembly.joints.len(), 1);
+}
+
 /// Two top faces mate face to face: B ends up upside down on A, not inside it;
 /// Flip turns it back over (into A).
 #[test]