diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index 4b55da026..20b2a923f 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -923,6 +923,11 @@ impl ConfigBuilder {
     }
 
     pub async fn build(self) -> std::io::Result<Config> {
+        // Keep the large config-loading future off small runtime thread stacks.
+        Box::pin(self.build_inner()).await
+    }
+
+    async fn build_inner(self) -> std::io::Result<Config> {
         let Self {
             codex_home,
             cli_overrides,