diff --git a/crates/ui-egui/src/panel_docking/tests.rs b/crates/ui-egui/src/panel_docking/tests.rs
index afae95ca0..1b8b1a168 100644
--- a/crates/ui-egui/src/panel_docking/tests.rs
+++ b/crates/ui-egui/src/panel_docking/tests.rs
@@ -321,6 +321,13 @@ fn the_tools_panel_docks_on_the_right_left_of_the_panels() {
     h.app.run("window.panel.float", json!({"panel": "tools"})).unwrap();
     assert_eq!(h.app.run("window.panel.dock", json!({"panel": "tools"})).unwrap()["side"], "right", "back on the side it docked at last");
     assert!(h.app.run("window.panel.dock", json!({"panel": "tools", "side": "top"})).is_err());
+    // A side that isn't text is an error too, not the last side: it leaves Tools where it is.
+    h.app.run("window.panel.float", json!({"panel": "tools"})).unwrap();
+    for side in [json!(5), json!(true), json!(["left"])] {
+        assert!(h.app.run("window.panel.dock", json!({"panel": "tools", "side": side})).is_err(), "{side}");
+        assert!(h.app.ui.toolbar_pos.is_some(), "still floating after side {side}");
+    }
+    assert_eq!(h.app.run("window.panel.dock", json!({"panel": "tools", "side": null})).unwrap()["side"], "right", "null: the last side");
 }
 
 /// The docked Tools panel as last drawn.
diff --git a/crates/ui-egui/src/tools_float.rs b/crates/ui-egui/src/tools_float.rs
index 2781e4232..0cc643342 100644
--- a/crates/ui-egui/src/tools_float.rs
+++ b/crates/ui-egui/src/tools_float.rs
@@ -219,12 +219,14 @@ pub(crate) fn command(app: &mut VectorcraftApp, id: &str, p: &Value) -> Option<R
         return None;
     }
     // Docking: on the left, or on the right left of the panels (default: the side it docked at last).
-    let right = match p.get("side").and_then(Value::as_str) {
-        None => Ok(app.ui.toolbar_right),
+    let right = match p.get("side") {
+        None | Some(Value::Null) => Ok(app.ui.toolbar_right),
         // `Start` and `End`, as panels take them, too.
-        Some(s) if s.eq_ignore_ascii_case("left") || s.eq_ignore_ascii_case("start") => Ok(false),
-        Some(s) if s.eq_ignore_ascii_case("right") || s.eq_ignore_ascii_case("end") => Ok(true),
-        Some(s) => Err(format!("side is left or right, not `{s}`")),
+        Some(Value::String(s)) if s.eq_ignore_ascii_case("left") || s.eq_ignore_ascii_case("start") => Ok(false),
+        Some(Value::String(s)) if s.eq_ignore_ascii_case("right") || s.eq_ignore_ascii_case("end") => Ok(true),
+        Some(Value::String(s)) => Err(format!("side is left or right, not `{s}`")),
+        // A number, a list…: an error, not the last side.
+        Some(v) => Err(format!("side is left or right, not `{v}`")),
     };
     Some(position(p).and_then(|at| {
         let right = right?;