diff --git a/.dagger/src/hephaestus_ci/main.py b/.dagger/src/hephaestus_ci/main.py
index b485922..0c89604 100644
--- a/.dagger/src/hephaestus_ci/main.py
+++ b/.dagger/src/hephaestus_ci/main.py
@@ -15,9 +15,10 @@ class HephaestusCi:
             dag.container()
             .from_("rust:1-bookworm")
             .with_exec(["rustup", "component", "add", "clippy", "rustfmt"])
-            # Cap parallel rustc — unbounded (= ncpu) spikes memory on heavy
-            # crates and OOMs the build engine on a many-core runner.
-            .with_env_variable("CARGO_BUILD_JOBS", "4")
+            # Serialize compilation (jobs=1) — even 4 parallel rustc invocations
+            # spike memory on heavy crates and OOM-kill the DinD build engine.
+            # Slower, but the runner survives; revisit if the host gets more RAM.
+            .with_env_variable("CARGO_BUILD_JOBS", "1")
             .with_mounted_cache(
                 "/usr/local/cargo/registry",
                 dag.cache_volume("heph-cargo-registry"),