diff --git a/core/VBA_check.m b/core/VBA_check.m
index cf74d9cc..30af062e 100644
--- a/core/VBA_check.m
+++ b/core/VBA_check.m
@@ -176,13 +176,14 @@
 gsi = find([options.sources.type]==0);
 for i=1:numel(gsi)
     for t=1:dim.n_t
-        diQ = diag(priors.iQy{t,i}).*~options.isYout(options.sources(gsi(i)).out,t);
-        options.isYout(options.sources(gsi(i)).out,t) = ~diQ;
-        priors.iQy{t,i} = diag(diQ)*priors.iQy{t,i}*diag(diQ);
+        diQ = (diag(priors.iQy{t,i}) == 0) || options.isYout(options.sources(gsi(i)).out,t);
+        options.isYout(options.sources(gsi(i)).out,t) = diQ;
+        priors.iQy{t,i} = diag(~diQ)*priors.iQy{t,i}*diag(~diQ);
     end
 end
 end
 
+
 % store evolution/observation function handles
 options.f_fname = f_fname;
 options.g_fname = g_fname;