diff --git a/siso.py b/siso.py
index 7e267cced4..38d34607b6 100644
--- a/siso.py
+++ b/siso.py
@@ -44,7 +44,9 @@ def parse_args(args):
 # Subcommand completes successfully if subcommand is present, returning 0,
 # and 2 if it's not present.
 def _is_subcommand_present(siso_path: str, subc: str) -> bool:
-    return subprocess.call([siso_path, "help", subc]) == 0
+    return subprocess.call([siso_path, "help", subc],
+                           stdout=subprocess.DEVNULL,
+                           stderr=subprocess.DEVNULL) == 0
 
 
 # Fetch PID platform independently of possibly running collector
diff --git a/tests/siso_test.py b/tests/siso_test.py
index 7dac8e9b4c..ddb6a7851f 100755
--- a/tests/siso_test.py
+++ b/tests/siso_test.py
@@ -70,7 +70,7 @@ ninja --failure_verbose=false -k=0
     @mock.patch('siso.subprocess.call')
     def test_is_subcommand_present(self, mock_call):
 
-        def side_effect(cmd):
+        def side_effect(cmd, *_, **__):
             if cmd[2] in ['collector', 'ninja']:
                 return 0
             return 2