diff --git a/src/expr.rs b/src/expr.rs
index 8dbe5c6d1dd..0beaee9dbf2 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -132,7 +132,7 @@ fn rewrite_call(context: &RewriteContext,
     }
 
     // 2 is for parens.
-    let remaining_width = width - callee_str.len() - 2;
+    let remaining_width = try_opt!(width.checked_sub(callee_str.len() + 2));
     let offset = callee_str.len() + 1 + offset;
 
     let items = itemize_list(context.codemap,
diff --git a/tests/target/fn.rs b/tests/target/fn.rs
index bc05efa5351..6c41f62a8b2 100644
--- a/tests/target/fn.rs
+++ b/tests/target/fn.rs
@@ -79,3 +79,17 @@ fn main() {
     let _ = function(move || 5);
     let _ = move || 42;
 }
+
+fn servo() {
+    let constellation_chan = Constellation::<layout::layout_task::LayoutTask,
+    script::script_task::ScriptTask>::start(
+        compositor_proxy,
+        resource_task,
+        image_cache_task,
+        font_cache_task,
+        time_profiler_chan,
+        mem_profiler_chan,
+        devtools_chan,
+        storage_task,
+        supports_clipboard);
+}