diff --git a/modoboa/lib/sysutils.py b/modoboa/lib/sysutils.py
index 7eb665493..221ef2b09 100644
--- a/modoboa/lib/sysutils.py
+++ b/modoboa/lib/sysutils.py
@@ -14,7 +14,7 @@ from django.utils.encoding import force_str
 
 
 def exec_cmd(
-    cmd: str | list[str],
+    cmd: list[str],
     sudo_user: str | None = None,
     pinput: str | None = None,
     capture_output: bool = True,
@@ -33,11 +33,7 @@ def exec_cmd(
     :return: return code, command output
     """
     if sudo_user is not None:
-        if isinstance(cmd, list):
-            cmd = ["sudo", "-u", sudo_user] + cmd
-        else:
-            cmd = f"sudo -u {sudo_user} {cmd}"
-
+        cmd = ["sudo", "-u", sudo_user] + cmd
     if pinput is not None:
         kwargs["stdin"] = subprocess.PIPE
     if capture_output:
diff --git a/tests.py b/tests.py
index 6a9e1a9ea..89b756b7d 100644
--- a/tests.py
+++ b/tests.py
@@ -26,10 +26,18 @@ class DeployTest(unittest.TestCase):
 
     def test_silent(self):
         dburl = f"default:{self.dbtype}://{self.dbuser}:{self.dbpassword}@{self.dbhost}:{self.dbport}/modoboa"
-        cmd = (
-            f"modoboa-admin.py deploy --collectstatic "
-            f"--dburl {dburl} --domain localhost --admin-username admin {self.projname}"
-        )
+        cmd = [
+            "modoboa-admin.py",
+            "deploy",
+            "--collectstatic",
+            "--dburl",
+            dburl,
+            "--domain",
+            "localhost",
+            "--admin-username",
+            "admin",
+            self.projname,
+        ]
         code, output = exec_cmd(cmd, cwd=self.workdir, shell=True)
         self.assertEqual(code, 0)