diff --git a/src/operator/rnn.cc b/src/operator/rnn.cc
index 74c563afceb1..7012a3c22f50 100644
--- a/src/operator/rnn.cc
+++ b/src/operator/rnn.cc
@@ -50,7 +50,7 @@ static bool RNNShape(const nnvm::NodeAttrs& attrs,
       "Needed input:[data, parameters, state], got in_shape->size(): " << in_shape->size();
   }
   const TShape &dshape = (*in_shape)[rnn_enum::kData];
-  if (dshape.ndim() ==  0) return false;
+  if (!mxnet::ndim_is_known(dshape)) return false;
   CHECK_EQ(dshape.ndim(), 3U) \
       << "Input data should be rank-3 tensor of dim [sequence length, batch size, input size]";
   // data: [sequence len, batch, input dimension]