diff --git a/openfisca_core/parameters/vectorial_parameter_node_at_instant.py b/openfisca_core/parameters/vectorial_parameter_node_at_instant.py
index 5022da954..160bd64ec 100644
--- a/openfisca_core/parameters/vectorial_parameter_node_at_instant.py
+++ b/openfisca_core/parameters/vectorial_parameter_node_at_instant.py
@@ -14,6 +14,8 @@ def __init__(self, vector, name, instant_str) -> None:
 
     @staticmethod
     def _get_appropriate_subnode_key(node, k):
+        if isinstance(k, numpy.integer):
+            return str(k)
         if isinstance(k, str):
             return k
         if isinstance(k, Enum):
diff --git a/tests/core/parameters_fancy_indexing/test_fancy_indexing.py b/tests/core/parameters_fancy_indexing/test_fancy_indexing.py
index 377372b73..f8eed1be6 100644
--- a/tests/core/parameters_fancy_indexing/test_fancy_indexing.py
+++ b/tests/core/parameters_fancy_indexing/test_fancy_indexing.py
@@ -154,6 +154,11 @@ def test_with_properties_starting_by_number() -> None:
     assert_near(P_2[city_code], [100, 300, 200])
 
 
+def test_with_integer() -> None:
+    city_code = numpy.asarray([75012, 75007, 75015])
+    assert_near(P_2[city_code], [100, 300, 200])
+
+
 P_3 = parameters.bareme("2015-01-01")