diff --git a/scripts/qemu_swarm.py b/scripts/qemu_swarm.py
index 2747eac1..3b1b0f0a 100644
--- a/scripts/qemu_swarm.py
+++ b/scripts/qemu_swarm.py
@@ -502,10 +502,14 @@ def start_aggregator(
     port: int, n_nodes: int, output_file: Path, log_file: Path
 ) -> Optional[subprocess.Popen]:
     """Start the Rust aggregator binary. Returns Popen or None on failure."""
+    import shutil
     cargo_toml = RUST_DIR / "Cargo.toml"
     if not cargo_toml.exists():
         warn(f"Rust workspace not found at {RUST_DIR}; skipping aggregator.")
         return None
+    if shutil.which("cargo") is None:
+        warn("cargo not found; skipping aggregator (Rust not installed).")
+        return None
 
     args = [
         "cargo", "run",