diff --git a/chempy/kinetics/rates.py b/chempy/kinetics/rates.py
index 54556bb4..9bc0e08d 100644
--- a/chempy/kinetics/rates.py
+++ b/chempy/kinetics/rates.py
@@ -198,8 +198,9 @@ def heaviside(x, z):
         elif hasattr(backend, 'clip'):  # e.g. numpy
             def heaviside(x, z):
                 assert z == 0
-                lx = backend.log(backend.maximum(x, tiny))
-                xclp = be.clip(lx, lo, hi)
+                lx = backend.log(backend.maximum(backend.array(x), tiny))
+                xclp = backend.clip(lx, lo, hi)
+                x = (xclp - lo)/(hi - lo)
                 y = (3 - 2*x)*x*x
                 return y
         else:
diff --git a/chempy/kinetics/tests/test__rates.py b/chempy/kinetics/tests/test__rates.py
index 3248c51a..489bde68 100644
--- a/chempy/kinetics/tests/test__rates.py
+++ b/chempy/kinetics/tests/test__rates.py
@@ -86,8 +86,8 @@ def test_Log10TPolyMassAction__units():
     p = MassAction(Constant(kunit)*10**ShiftedTPoly([273.15*u.K, .7, .02/u.K, .003/u.K**2, .0004/u.K**3]))
     r = Reaction({'A': 2, 'B': 1}, {'C': 1}, p, {'B': 1})
     res = p({'A': 11*u.molar, 'B': 13*u.molar, 'temperature': 298.15*u.K}, reaction=r)
-    ref = 10**(.7 + .02*25 + 0.003 * 25**2 + 0.0004 * 25**3)
-    assert abs(res - ref*13*11**2*Mps) < 1e-15
+    ref = 10**(.7 + .02*25 + 0.003 * 25**2 + 0.0004 * 25**3)*13*11**2*Mps
+    assert abs((res - ref)/ref) < 1e-15
 
 
 def test_TPolyInLog10MassAction():
diff --git a/chempy/tests/test_units.py b/chempy/tests/test_units.py
index 7a4e0c09..c6224852 100644
--- a/chempy/tests/test_units.py
+++ b/chempy/tests/test_units.py
@@ -207,7 +207,7 @@ def test_to_unitless():
     sy.exp(Ea_over_RT_uncert)
 
     T_K_sym = np.array(sy.Symbol('T_K', real=True), dtype=object) * u.K
-    to_unitless(T_K_sym/(298*u.K))
+    assert to_unitless(T_K_sym/(298*u.K)).tolist() == [sy.Symbol('T_K', real=True)]
     rescale(simplified(Ea/dc.molar_gas_constant)/T_K_sym, 1)
     Ea_over_R_uncert = UncertainQuantity(Ea, unit_of(Ea), 0.1*Ea)/dc.molar_gas_constant
     to_unitless(Ea_over_R_uncert/(298*u.K))
@@ -223,7 +223,7 @@ def test_UncertainQuantity():
     a = UncertainQuantity([1, 2], u.m, [.1, .2])
     assert a[1] == [2.]*u.m
     assert (-a)[0] == [-1.]*u.m
-    assert (-a).uncertainty[0] == [0.1]*u.m
+    assert allclose((-a).uncertainty[0], [0.1]*u.m)
     assert (-a)[0] == (a*-1)[0]
     assert (-a).uncertainty[0] == (a*-1).uncertainty[0]
     assert allclose(a, [1, 2]*u.m)