diff --git a/pde/tools/expressions.py b/pde/tools/expressions.py
index bae80ee7..c8a3c26d 100644
--- a/pde/tools/expressions.py
+++ b/pde/tools/expressions.py
@@ -282,11 +282,11 @@ def __eq__(self, other):
             return False
 
         # compare the expressions themselves by checking their difference
-        diff = sympy.simplify(self._sympy_expr - other._sympy_expr)
+        difference = sympy.simplify(self._sympy_expr - other._sympy_expr)
         if isinstance(self._sympy_expr, sympy.NDimArray):
-            return diff == sympy.Array(np.zeros(self._sympy_expr.shape))
+            return difference == sympy.Array(np.zeros(self._sympy_expr.shape, int))
         else:
-            return diff == 0
+            return difference == 0
 
     @property
     def _free_symbols(self) -> set:
diff --git a/tests/tools/test_expressions.py b/tests/tools/test_expressions.py
index 9cccdffa..ba583eb3 100644
--- a/tests/tools/test_expressions.py
+++ b/tests/tools/test_expressions.py
@@ -218,7 +218,7 @@ def test_tensor_expression():
     assert e.constant
     np.testing.assert_allclose(e.get_compiled_array()(), [[0, 1], [2, 3]])
     np.testing.assert_allclose(e.get_compiled_array()(tuple()), [[0, 1], [2, 3]])
-    assert e.differentiate("a") == TensorExpression("[[0., 0.], [0., 0.]]")
+    assert e.differentiate("a") == TensorExpression("[[0, 0], [0, 0]]")
     np.testing.assert_allclose(e.value, np.arange(4).reshape(2, 2))
 
     e = TensorExpression("[a, 2*a]")