diff --git a/swash/processing/swash.py b/swash/processing/swash.py
index 1a739a8..1fb78df 100644
--- a/swash/processing/swash.py
+++ b/swash/processing/swash.py
@@ -46,14 +46,14 @@ with tempfile.TemporaryDirectory(prefix="swash_", dir=".") as tmp_raw:
         cmd = (config.get("swash", "swashrun"), "-input", inp.name, *mpi)
         log.info(f"Running {cmd}")
 
-        subprocess.Popen(
+        swash_run = subprocess.Popen(
             cmd,
             cwd=tmpdir,
             stdout=logfile,
             stderr=logfile,
         )
 
-        code = subprocess.wait()
+        code = swash_run.wait()
         if code is not 0:
             log.error(f"Swash returned error code {code}")