diff --git a/crates/agent_ui/src/conversation_view/thread_view.rs b/crates/agent_ui/src/conversation_view/thread_view.rs
index 6300ac15402..c9ef4921542 100644
--- a/crates/agent_ui/src/conversation_view/thread_view.rs
+++ b/crates/agent_ui/src/conversation_view/thread_view.rs
@@ -3300,6 +3300,7 @@ impl ThreadView {
             .child(
                 v_flex()
                     .when_some(max_content_width, |this, max_w| this.flex_basis(max_w))
+                    .when(max_content_width.is_none(), |this| this.w_full())
                     .when(fills_container, |this| this.h_full())
                     .flex_shrink()
                     .flex_grow_0()