diff --git a/clstm.cc b/clstm.cc
index 0b0cadd..7a76700 100644
--- a/clstm.cc
+++ b/clstm.cc
@@ -877,7 +877,8 @@ struct GenericNPLSTM : NetworkBase {
       backward_statemem(state[t], ci[t], gi[t], state, t-1, gf[t]);
       gradient_clip(state[t].d, gradient_clipping);
       backward_full<F>(gi[t], WGI, source[t], gradient_clipping);
-      if (t>0) backward_full<F>(gf[t], WGF, source[t], gradient_clipping);
+      assert(gf[0].d.maxCoeff()==0);
+      backward_full<F>(gf[t], WGF, source[t], gradient_clipping);
       backward_full<F>(go[t], WGO, source[t], gradient_clipping);
       backward_full<G>(ci[t], WCI, source[t], gradient_clipping);
       backward_stack1(source[t], inputs[t], out, t-1);