diff --git a/fast_oopsi.m b/fast_oopsi.m
index 7b420e1..2ca8070 100755
--- a/fast_oopsi.m
+++ b/fast_oopsi.m
@@ -64,6 +64,14 @@
 % P_best:   inferred parameter structure
 % V:        structure of Variables for algorithm to run
 
+
+
+%% check data
+
+if any(isnan(F));
+    error('nan in your data')
+end
+
 %% initialize algorithm Variables
 starttime   = cputime;
 siz         = size(F);      if siz(2)==1, F=F'; siz=size(F); end
diff --git a/run_oopsi.m b/run_oopsi.m
index 7f657ef..cb2c9e0 100755
--- a/run_oopsi.m
+++ b/run_oopsi.m
@@ -20,6 +20,13 @@
 %   fast:   fast-oopsi MAP estimate of spike train, argmax_{n\geq 0} P[n|F], (fast.n),  parameter estimate (fast.P), and structure of  variables for algorithm (fast.V)
 %   smc:    smc-oopsi estimate of {P[X_t|F]}_{t<T}, where X={n,C} or {n,C,h}, (smc.E), parameter estimates (smc.P), and structure of variables for algorithm (fast.V)
 
+%% check data
+
+if any(isnan(F));
+    error('nan in your data')
+end
+
+
 %% set code Variables
 
 if nargin < 2, V = struct;   end         % create structure for algorithmic variables, if none provided
@@ -64,6 +71,8 @@
     save(V.name_dat,'V')
 end
 
+
+
 %% preprocess - remove the lowest 10 frequencies
 
 if V.preprocess==1