diff --git a/gnm/shape/gnm_numpy_test.py b/gnm/shape/gnm_numpy_test.py
index 57b2167..a74bb6c 100644
--- a/gnm/shape/gnm_numpy_test.py
+++ b/gnm/shape/gnm_numpy_test.py
@@ -429,6 +429,9 @@ def test_edge_list(self, version: str, variant: str):
     np.testing.assert_array_equal(
         adjacency_matrix_quads, adjacency_matrix_edge_list
     )
+    self.assertLen(
+        gnm_np.edge_list, len(np.unique(gnm_np.edge_list, axis=0))
+    )
 
   @parameterized.parameters(get_group_subsets_test_cases())
   def test_group_subsets(self, version: str, variant: str, group_name: str):
diff --git a/gnm/shape/gnm_xnp.py b/gnm/shape/gnm_xnp.py
index 396384e..211d1fd 100644
--- a/gnm/shape/gnm_xnp.py
+++ b/gnm/shape/gnm_xnp.py
@@ -426,7 +426,7 @@ def edge_list(self) -> npt.NDArray[np.integer]:
     e1 = quads.ravel()
     e2 = np.roll(quads, -1, axis=1).ravel()
     edges = np.stack([np.minimum(e1, e2), np.maximum(e1, e2)], axis=1)
-    edge_keys = e1 + self.num_vertices * e2
+    edge_keys = edges[:, 0] + self.num_vertices * edges[:, 1]
     _, unique_indices = np.unique(edge_keys, return_index=True)
     unique_undirected_edges = edges[unique_indices]
     return np.vstack(