diff --git a/pytket/tests/classical_test.py b/pytket/tests/classical_test.py
index e20886482b..c3b38c4672 100644
--- a/pytket/tests/classical_test.py
+++ b/pytket/tests/classical_test.py
@@ -497,9 +497,9 @@ def test_wasm_argtypes() -> None:
 
     cmd = c.get_commands()[0]
 
-    assert cmd.args[0].isinstance(unit_id.Bit)
-    assert cmd.args[1].isinstance(unit_id.Bit)
-    assert cmd.args[2].isinstance(unit_id.WasmState)
+    assert isinstance(cmd.args[0], unit_id.Bit)
+    assert isinstance(cmd.args[1], unit_id.Bit)
+    assert isinstance(cmd.args[2], unit_id.WasmState)
 
 
 def test_wasm_uid_from_circuit() -> None: