diff --git a/ndonnx/_core/_interface.py b/ndonnx/_core/_interface.py
index 9e89ca9..23bb388 100644
--- a/ndonnx/_core/_interface.py
+++ b/ndonnx/_core/_interface.py
@@ -345,6 +345,9 @@ def permute_dims(self, x, axes) -> ndx.Array:
     def reshape(self, x, shape, *, copy=None) -> ndx.Array:
         return NotImplemented
 
+    def repeat(self, x, repeats, axis=None) -> ndx.Array:
+        return NotImplemented
+
     def roll(self, x, shift, axis) -> ndx.Array:
         return NotImplemented
 
diff --git a/ndonnx/_core/_shapeimpl.py b/ndonnx/_core/_shapeimpl.py
index 436208f..5004953 100644
--- a/ndonnx/_core/_shapeimpl.py
+++ b/ndonnx/_core/_shapeimpl.py
@@ -66,7 +66,7 @@ def expand_dims(self, x, axis):
             )
         )
 
-    def repeat(self, x, repeats, axis):
+    def repeat(self, x, repeats, axis=None):
         if axis is None:
             x = ndx.reshape(x, [-1])
             axis = 0