diff --git a/tests/test_backend.py b/tests/test_backend.py
index 1060574c1..225f9461a 100755
--- a/tests/test_backend.py
+++ b/tests/test_backend.py
@@ -1685,6 +1685,23 @@ def func(x1, x2, x3):
             return tf.identity(x_, name=_TFOUTPUT)
         self._run_test_case(func, [_OUTPUT], {_INPUT: x_val1, _INPUT1: x_val2, "input3:0": x_val3})
 
+    def test_concat_negative_axis_none_shape(self):
+        x_val = np.array([1.0, 2.0, 3.0, 4.0, 5.0, 6.0], dtype=np.float32).reshape((2, 3))
+        y_val = np.array([7.0, 8.0, 9.0, 10.0, 11.0, 12.0], dtype=np.float32).reshape((2, 3))
+        s1_val = np.array([1, 1], dtype=np.int32)
+        s2_val = np.array([1, 1], dtype=np.int32)
+        def func():
+            x = tf_placeholder(tf.float32, [2, 3], name=_TFINPUT)
+            y = tf_placeholder(tf.float32, [2, 3], name=_TFINPUT1)
+            s1 = tf_placeholder(tf.int32, [2], name="input3")
+            s2 = tf_placeholder(tf.int32, [2], name="input4")
+            s = tf.add(s1, s2)
+            x_with_none_shape = tf.slice(x, [0, 0], s)
+            t = tf.concat([x_with_none_shape, y], -1)
+            return tf.identity(t, name=_TFOUTPUT)
+        self._run_test_case(func, [_OUTPUT], {_INPUT: x_val, _INPUT1: y_val, "input3:0": s1_val, "input4:0": s2_val},
+                            as_session=True, premade_placeholders=True)
+
     def test_concat_const_string(self):
         x_val1 = np.array([["Hello world", "abc"], ["def", "♦♥♠♣"]], dtype=str)
         const_val = np.array([["Hello there", "wxyz"], ["", "π"]], dtype=str)
diff --git a/tf2onnx/onnx_opset/tensor.py b/tf2onnx/onnx_opset/tensor.py
index ca4daf0d1..bb9b0cb52 100644
--- a/tf2onnx/onnx_opset/tensor.py
+++ b/tf2onnx/onnx_opset/tensor.py
@@ -297,8 +297,13 @@ def version_1(cls, ctx, node, **kwargs):
         ctx.remove_input(node, node.input[-1], len(node.input) - 1)
 
         if axis_val < 0:  # onnxruntime does not support -1 axis, but TF supports.
-            input_shape = ctx.get_shape(node.input[0])
-            utils.make_sure(input_shape is not None, "shape of {} is None".format(node.input[0]))
+            input_shape = None
+            for node_input in node.input:
+                input_shape = ctx.get_shape(node_input)
+                if input_shape is not None:
+                    break
+            utils.make_sure(input_shape is not None,
+                            "the shapes of the following inputs are None: {}".format(', '.join(node.input)))
             axis_val = len(input_shape) + axis_val
         node.set_attr("axis", axis_val)