diff --git a/frc971/control_loops/python/BUILD b/frc971/control_loops/python/BUILD
index bb2a754..fa94d01 100644
--- a/frc971/control_loops/python/BUILD
+++ b/frc971/control_loops/python/BUILD
@@ -9,6 +9,7 @@
     'libcdd.py',
   ],
   deps = [
+    '//external:python-glog',
     '//external:slycot',
   ],
   data = [
diff --git a/frc971/control_loops/python/controls.py b/frc971/control_loops/python/controls.py
index 6494ce1..8a63620 100644
--- a/frc971/control_loops/python/controls.py
+++ b/frc971/control_loops/python/controls.py
@@ -12,6 +12,7 @@
 import numpy
 import slycot
 import scipy.signal.cont2discrete
+import glog
 
 class Error (Exception):
   """Base class for all control loop exceptions."""
@@ -94,7 +95,7 @@
 def ctrb(A, B):
   """Returns the controlability matrix.
 
-    This matrix must have full rank for all the states to be controlable.
+    This matrix must have full rank for all the states to be controllable.
   """
   n = A.shape[0]
   output = B
@@ -133,9 +134,16 @@
   """
   I = numpy.matrix(numpy.eye(Q.shape[0]))
   Z = numpy.matrix(numpy.zeros(Q.shape[0]))
+  n = A.shape[0]
+  m = C.shape[0]
+
+  controllability_rank = numpy.linalg.matrix_rank(ctrb(A.T, C.T))
+  if controlability_rank != n:
+    glog.warning('Observability of %d != %d, unobservable state',
+                 controlability_rank, n)
 
   # Compute the steady state covariance matrix.
-  P_prior = scipy.linalg.solve_discrete_are(A.T, C.T, Q, R)
+  P_prior, rcond, w, S, T = slycot.sb02od(n=n, m=m, A=A.T, B=C.T, Q=Q, R=R, dico='D')
   S = C * P_prior * C.T + R
   K = numpy.linalg.lstsq(S.T, (P_prior * C.T).T)[0].T
   P = (I - K * C) * P_prior