diff --git a/crates/doc/src/ids_tests.rs b/crates/doc/src/ids_tests.rs
--- a/crates/doc/src/ids_tests.rs
+++ b/crates/doc/src/ids_tests.rs
@@ -110,3 +110,11 @@ fn the_highest_space_counts_every_kind_of_id() {
     assert_eq!(id_space("S:99999999999999999999999", "S:"), 0, "too big for a number");
     assert_eq!(mode_number("1:0"), None);
 }
+
+#[test]
+fn nodeid_rejects_plus_sign() {
+    assert!("+12".parse::<crate::NodeId>().is_err());
+    assert!("0:+12".parse::<crate::NodeId>().is_err());
+    assert_eq!("12".parse::<crate::NodeId>(), Ok(crate::NodeId(12)));
+    assert_eq!("0:12".parse::<crate::NodeId>(), Ok(crate::NodeId(12)));
+}
diff --git a/crates/doc/src/lib.rs b/crates/doc/src/lib.rs
--- a/crates/doc/src/lib.rs
+++ b/crates/doc/src/lib.rs
@@ -67,6 +67,10 @@ impl std::str::FromStr for NodeId {
         // Accept "12" and Figma-style "0:12".
         let t = s.trim();
         let t = t.rsplit(':').next().unwrap_or(t);
+        if t.starts_with('+') {
+            // `u64::parse` accepts a leading '+'; ids are digits only.
+            return "-".parse::<u64>().map(NodeId);
+        }
         t.parse::<u64>().map(NodeId)
     }
 }