diff --git a/crates/engine/src/cmd/stroke.rs b/crates/engine/src/cmd/stroke.rs
index d397056ad..de4051e9a 100644
--- a/crates/engine/src/cmd/stroke.rs
+++ b/crates/engine/src/cmd/stroke.rs
@@ -100,7 +100,12 @@ impl StrokeChange {
         let dash = match p.get("dash") {
             None => None,
             Some(Value::Null) => Some(None),
-            Some(Value::Array(a)) => Some(Some(a.iter().filter_map(Value::as_f64).collect::<Vec<_>>()).filter(|d| !d.is_empty())),
+            Some(Value::Array(a)) => {
+                // Do not silently omit malformed segments and change the user's dash pattern.
+                let values: Vec<f64> =
+                    a.iter().map(|v| v.as_f64().ok_or_else(|| bad(cmd, format!("dash lengths must be numbers, got {v}")))).collect::<Result<_>>()?;
+                Some(Some(values).filter(|d| !d.is_empty()))
+            }
             Some(v) => return Err(bad(cmd, format!("dash must be a list of lengths or null, got {v}"))),
         };
         Ok(Self {
@@ -167,9 +172,6 @@ fn no_targets(ids: &[vectorcraft_doc::NodeId], p: &Value) -> bool {
 fn stroke_set(s: &mut Session, p: &Value) -> Result<Value> {
     const C: &str = "stroke.set";
     let change = StrokeChange::parse(p, C)?;
-    if let Some(w) = change.weight {
-        s.paint.stroke_width = w;
-    }
     let item = item_target(s, p, C)?.of_kind(s, false);
     let mut ids = item.targets(s, p)?;
     let new_art = no_targets(&ids, p);
@@ -216,10 +218,6 @@ fn stroke_set(s: &mut Session, p: &Value) -> Result<Value> {
             st.profile = pr.clone();
         }
     };
-    // With nothing selected the Stroke panel sets up the next object drawn.
-    if new_art && let Some(st) = s.new_art_stroke_mut() {
-        set(st);
-    }
     edit_items(s, &ids, item, C, "Stroke", false, |n, index| {
         if index.is_none()
             && let NodeKind::Text(t) = &mut n.kind
@@ -235,6 +233,14 @@ fn stroke_set(s: &mut Session, p: &Value) -> Result<Value> {
         }
         Ok(())
     })?;
+    // Commit the new-art template only after the complete request is validated
+    // and the selected artwork edit has succeeded.
+    if let Some(w) = change.weight {
+        s.paint.stroke_width = w;
+    }
+    if new_art && let Some(st) = s.new_art_stroke_mut() {
+        set(st);
+    }
     ok()
 }
 
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 69c4ce756..1a45a94e1 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -134,6 +134,41 @@ fn fill_and_stroke_commands() {
     s.execute("paint.setFill", &json!({"gradient": {"kind": "radial"}})).unwrap();
 }
 
+#[test]
+fn stroke_rejects_invalid_dash_components_and_preserves_defaults_on_error() {
+    let mut s = session();
+    let id = rect(&mut s, 0.0, 0.0, 40.0, 30.0);
+    s.execute("stroke.set", &json!({"weight": 3, "dash": [6, 3]})).unwrap();
+    let previous_weight = s.paint.stroke_width;
+    let previous_stroke = s.doc().unwrap().doc.node(id).unwrap().appearance.stroke().cloned();
+
+    for params in [
+        json!({"weight": 10, "dash": [6, "not a number", 3]}),
+        json!({"weight": 10, "ids": "not an array"}),
+        json!({"weight": 10, "item": "invalid"}),
+        json!({"weight": 10, "arrowAlign": "unknown"}),
+    ] {
+        assert!(s.execute("stroke.set", &params).is_err(), "{params} must fail");
+        assert_eq!(s.paint.stroke_width, previous_weight, "failed stroke edit changed new-art defaults");
+        assert_eq!(s.doc().unwrap().doc.node(id).unwrap().appearance.stroke().cloned(), previous_stroke);
+    }
+
+    // A valid dash list still updates the selected stroke and new-art default width.
+    s.execute("stroke.set", &json!({"weight": 7, "dash": [4, 2]})).unwrap();
+    assert_eq!(s.paint.stroke_width, 7.0);
+    assert_eq!(s.doc().unwrap().doc.node(id).unwrap().appearance.stroke().unwrap().width, 7.0);
+
+    // With nothing selected the panel sets up the next object drawn: a rejected edit doesn't.
+    s.execute("select.none", &json!({})).unwrap();
+    let next = s.new_art();
+    assert!(s.execute("stroke.set", &json!({"weight": 12, "dash": [2, 2], "arrowAlign": "unknown"})).is_err());
+    assert_eq!(s.new_art(), next);
+    s.execute("stroke.set", &json!({"weight": 12, "dash": [2, 2]})).unwrap();
+    let next = s.new_art();
+    let stroke = next.stroke().unwrap();
+    assert_eq!((stroke.width, stroke.dash.as_ref().map(|d| d.pattern.clone())), (12.0, Some(vec![2.0, 2.0])));
+}
+
 #[test]
 fn rejected_paint_edits_leave_new_art_defaults_and_focus_unchanged() {
     let mut s = session();