diff --git a/crates/engine/src/cmd/style.rs b/crates/engine/src/cmd/style.rs
index e0eee77b9..0ff7c8a4f 100644
--- a/crates/engine/src/cmd/style.rs
+++ b/crates/engine/src/cmd/style.rs
@@ -1515,7 +1515,7 @@ fn create_object(s: &mut Session, p: &Value) -> Result<Value> {
     if let Some(f) = fill_param(CREATE, p, os.fill.as_ref())? {
         os.fill = f;
     }
-    if let Some(st) = group_param(CREATE, p, "stroke", os.stroke.as_ref().unwrap_or(&designcraft_doc::Stroke::default()))? {
+    if let Some(st) = stroke_param(CREATE, p, os.stroke.as_ref())? {
         os.stroke = st;
     }
     if let Some(c) = corners_param(CREATE, p, os.corners.unwrap_or_default())? {
@@ -1535,6 +1535,18 @@ fn create_object(s: &mut Session, p: &Value) -> Result<Value> {
     })
 }
 
+/// `p.stroke` merged over `base` (as [`group_param`]), refused when the weight isn't a number ≥ 0
+/// or the tint isn't finite.
+fn stroke_param(cmd: &str, p: &Value, base: Option<&designcraft_doc::Stroke>) -> Result<Option<Option<designcraft_doc::Stroke>>> {
+    let st = group_param(cmd, p, "stroke", base.unwrap_or(&designcraft_doc::Stroke::default()))?;
+    if let Some(Some(st)) = &st
+        && !(st.weight.is_finite() && st.weight >= 0.0 && st.tint.is_finite())
+    {
+        return Err(bad(cmd, "stroke weight must be a number ≥ 0"));
+    }
+    Ok(st)
+}
+
 /// `p[key]`, an attribute group of a style, merged field by field over `base`: `None` when not
 /// given, `Some(None)` for null (the style no longer sets it).
 fn group_param<T: serde::Serialize + serde::de::DeserializeOwned>(cmd: &str, p: &Value, key: &str, base: &T) -> Result<Option<Option<T>>> {
@@ -1616,12 +1628,7 @@ fn edit_object(s: &mut Session, p: &Value) -> Result<Value> {
     if let Some(f) = fill_param(CMD, p, old.fill.as_ref())? {
         new.fill = f;
     }
-    if let Some(st) = group_param(CMD, p, "stroke", old.stroke.as_ref().unwrap_or(&designcraft_doc::Stroke::default()))? {
-        if let Some(st) = &st
-            && !(st.weight.is_finite() && st.weight >= 0.0 && st.tint.is_finite())
-        {
-            return Err(bad(CMD, "stroke weight must be a number ≥ 0"));
-        }
+    if let Some(st) = stroke_param(CMD, p, old.stroke.as_ref())? {
         new.stroke = st;
     }
     if let Some(c) = corners_param(CMD, p, old.corners.unwrap_or_default())? {
diff --git a/crates/engine/src/tests.rs b/crates/engine/src/tests.rs
index 47bfcb523..0441f9bd9 100644
--- a/crates/engine/src/tests.rs
+++ b/crates/engine/src/tests.rs
@@ -725,6 +725,13 @@ fn object_styles_carry_corners_and_their_stroke_and_corners_can_be_edited() {
     assert!(s.execute("style.object.edit", &json!({"name": "Framed", "rename": "[Basic Text Frame]"})).is_err());
     assert!(s.execute("style.object.edit", &json!({"name": "[Basic Graphics Frame]", "rename": "Mine"})).is_err());
     assert!(s.execute("style.object.edit", &json!({"name": "Framed", "corners": {"size": "big"}})).is_err());
+    // A negative stroke weight is refused when creating a style as when editing one.
+    let styles = s.doc().unwrap().doc.styles.object.len();
+    for cmd in ["style.object.create", "style.object.edit"] {
+        let e = s.execute(cmd, &json!({"name": "Framed", "stroke": {"weight": -3}})).unwrap_err();
+        assert!(e.to_string().contains("stroke weight"), "{cmd}: {e}");
+    }
+    assert_eq!(s.doc().unwrap().doc.styles.object.len(), styles);
     // null: the style stops setting corners, the items keep theirs.
     s.execute("style.object.edit", &json!({"name": "Framed", "corners": null})).unwrap();
     assert!(s.doc().unwrap().doc.styles.object_style("Framed").unwrap().corners.is_none());