diff --git a/stl/fastboolean_eval.py b/stl/fastboolean_eval.py
index 6c8091e..f6d69b4 100644
--- a/stl/fastboolean_eval.py
+++ b/stl/fastboolean_eval.py
@@ -8,6 +8,7 @@ import numpy as np
 import sympy as smp
 from lenses import lens
 import gmpy2 as gp
+from bitarray import bitarray
 
 import stl.ast
 
@@ -19,20 +20,21 @@ def pointwise_sat(stl):
 @pointwise_sat.register(stl.Or)
 def _(stl):
     def sat_comp(x,t):
-        val = 0
+        sat = bitarray(len(t))
         for arg in stl.args:
-            val = pointwise_sat(arg)(x, t) | val
-        return val
+            sat = pointwise_sat(arg)(x, t) | sat
+        return sat
     return sat_comp
 
 
 @pointwise_sat.register(stl.And)
 def _(stl):
     def sat_comp(x,t):
-        val = 2**(len(t))-1
+        sat = bitarray(len(t))
+        sat.setall('True')
         for arg in stl.args:
-            val = pointwise_sat(arg)(x, t) & val
-        return val
+            sat = pointwise_sat(arg)(x, t) & sat
+        return sat
     return sat_comp
 
 
@@ -40,11 +42,11 @@ def _(stl):
 def _(stl):
     lo, hi = stl.interval
     def sat_comp(x,t):
-        val = 0
+        sat = bitarray()
         for tau in t:
             tau_t = [min(tau + t2, x.index[-1]) for t2 in x[lo:hi].index]
-            val = (val << 1) | (pointwise_sat(stl.arg)(x, tau_t) > 0)
-        return val
+            sat.append((pointwise_sat(stl.arg)(x, tau_t)).count() > 0)
+        return sat
     return sat_comp
 
 
@@ -52,20 +54,18 @@ def _(stl):
 def _(stl):
     lo, hi = stl.interval
     def sat_comp(x,t):
-        val = 0
+        sat = bitarray()
         for tau in t:
             tau_t = [min(tau + t2, x.index[-1]) for t2 in x[lo:hi].index]
-            val = (val << 1) | (gp.popcount(pointwise_sat(stl.arg)(x, tau_t)) == len(tau_t))
-        return val
+            point_sat = pointwise_sat(stl.arg)(x, tau_t)
+            sat.append(point_sat.count() == point_sat.length())
+        return sat
     return sat_comp
 
 
 @pointwise_sat.register(stl.Neg)
 def _(stl):
-    def sat_comp(x,t):
-        val = pointwise_sat(arg)(x, t) ^ (2**(len(t))-1)
-        return val
-    return sat_comp
+    return lambda x,t: ~pointwise_sat(arg)(x, t) 
 
 
 op_lookup = {
@@ -80,10 +80,9 @@ op_lookup = {
 @pointwise_sat.register(stl.AtomicPred)
 def _(stl):
     def sat_comp(x, t):
-        val = 0
-        for tau in t:
-            val = (val << 1) | (1 if x[stl.id][tau] else 0)
-        return val
+        sat = bitarray()
+        [sat.append(x[stl.id][tau]) for tau in t]
+        return sat
     return sat_comp
 
 
@@ -91,10 +90,9 @@ def _(stl):
 def _(stl):
     op = op_lookup[stl.op]
     def sat_comp(x, t):
-        val = 0
-        for tau in t:
-            val = (val << 1) | (op(eval_terms(stl, x, tau), stl.const) == True)
-        return val
+        sat = bitarray()
+        [sat.append(op(eval_terms(stl, x, tau), stl.const)) for tau in t]
+        return sat
     return sat_comp 
 
 
diff --git a/stl/test_fastboolean_eval.py b/stl/test_fastboolean_eval.py
new file mode 100644
index 0000000..043d754
--- /dev/null
+++ b/stl/test_fastboolean_eval.py
@@ -0,0 +1,25 @@
+import stl
+import stl.fastboolean_eval
+import pandas as pd
+from nose2.tools import params
+import unittest
+from sympy import Symbol
+
+ex1 = ("2*A > 3", False)
+ex2 = ("F[0, 1](2*A > 3)", True)
+ex3 = ("F[1, 0](2*A > 3)", False)
+ex4 = ("G[1, 0](2*A > 3)", True)
+ex5 = ("(A < 0)", False)
+ex6 = ("G[0, 0.1](A < 0)", False)
+ex7 = ("G[0, 0.1](C)", True)
+ex8 = ("G[0, 0.2](C)", False)
+ex9 = ("(F[0, 0.2](C)) and (F[0, 1](2*A > 3))", True)
+x = pd.DataFrame([[1,2, True], [1,4, True], [4,2, False]], index=[0,0.1,0.2], 
+                 columns=["A", "B", "C"])
+
+class TestSTLRobustness(unittest.TestCase):
+    @params(ex1, ex2, ex3, ex4, ex5, ex6, ex7, ex8, ex9)
+    def test_stl(self, phi_str, r):
+        phi = stl.parse(phi_str)
+        stl_eval = stl.fastboolean_eval.pointwise_sat(phi)
+        self.assertEqual(stl_eval(x, [0]), r)