diff --git a/python/ribasim/ribasim/geometry/edge.py b/python/ribasim/ribasim/geometry/edge.py
index 4fb268dfe..f0c42b6fd 100644
--- a/python/ribasim/ribasim/geometry/edge.py
+++ b/python/ribasim/ribasim/geometry/edge.py
@@ -101,6 +101,10 @@ def add(
         self.df = GeoDataFrame[EdgeSchema](
             pd.concat([self.df, table_to_append], ignore_index=True)
         )
+        if self.df.duplicated(subset=["from_node_id", "to_node_id"]).any():
+            raise ValueError(
+                f"Edges have to be unique, but edge ({from_node.node_id}, {to_node.node_id}) already exists."
+            )
         self.df.index.name = "fid"
 
     def _get_where_edge_type(self, edge_type: str) -> NDArray[np.bool_]:
diff --git a/python/ribasim/tests/test_model.py b/python/ribasim/tests/test_model.py
index 734c8121f..db249f0a4 100644
--- a/python/ribasim/tests/test_model.py
+++ b/python/ribasim/tests/test_model.py
@@ -141,6 +141,19 @@ def test_edge_table(basic):
     assert df.crs == CRS.from_epsg(28992)
 
 
+def test_duplicate_edge(trivial):
+    model = trivial
+    with pytest.raises(
+        ValueError,
+        match=re.escape("Edges have to be unique, but edge (6, 0) already exists."),
+    ):
+        model.edge.add(
+            model.basin[6],
+            model.tabulated_rating_curve[0],
+            name="duplicate",
+        )
+
+
 def test_indexing(basic):
     model = basic