diff --git a/swash/processing/swash.py b/swash/processing/swash.py
index fa30723..7521341 100644
--- a/swash/processing/swash.py
+++ b/swash/processing/swash.py
@@ -54,7 +54,7 @@ with tempfile.TemporaryDirectory(prefix="swash_", dir=".") as tmp_raw:
         )
 
         code = swash_run.wait()
-        if code is not 0:
+        if code != 0:
             log.error(f"Swash returned error code {code}")
 
     log.info(f"Moving swash output to '{out}'")