diff --git a/tests/data/nomenclature_configs/multiple_repos_for_mapping.yaml b/tests/data/nomenclature_configs/multiple_repos_for_mapping.yaml
new file mode 100644
index 00000000..ff2bd784
--- /dev/null
+++ b/tests/data/nomenclature_configs/multiple_repos_for_mapping.yaml
@@ -0,0 +1,9 @@
+repositories:
+  common-definitions:
+    url: https://github.com/IAMconsortium/common-definitions.git/
+  legacy-definitions:
+    url: https://github.com/IAMconsortium/legacy-definitions.git/
+mappings:
+  repositories:
+    - common-definitions
+    - legacy-definitions
diff --git a/tests/data/nomenclature_configs/multiple_repos_per_dimension.yaml b/tests/data/nomenclature_configs/multiple_repos_per_dimension.yaml
new file mode 100644
index 00000000..6e510cd2
--- /dev/null
+++ b/tests/data/nomenclature_configs/multiple_repos_per_dimension.yaml
@@ -0,0 +1,10 @@
+repositories:
+  common-definitions:
+    url: https://github.com/IAMconsortium/common-definitions.git/
+  legacy-definitions:
+    url: https://github.com/IAMconsortium/legacy-definitions.git/
+definitions:
+  variable:
+    repository:
+      - common-definitions
+      - legacy-definitions
diff --git a/tests/data/nomenclature_configs/variable/.gitkeep b/tests/data/nomenclature_configs/variable/.gitkeep
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/test_codelist.py b/tests/test_codelist.py
index 4fd0a5c0..5668bc65 100644
--- a/tests/test_codelist.py
+++ b/tests/test_codelist.py
@@ -3,15 +3,16 @@
 import pandas.testing as pdt
 import logging
 
-from nomenclature.code import Code, RegionCode, MetaCode, VariableCode
+from nomenclature.code import Code, RegionCode, MetaCode
 from nomenclature.codelist import (
     CodeList,
     VariableCodeList,
     RegionCodeList,
     MetaCodeList,
 )
+from nomenclature.config import NomenclatureConfig
 
-from conftest import TEST_DATA_DIR
+from conftest import TEST_DATA_DIR, clean_up_external_repos
 
 
 def test_simple_codelist():
@@ -323,3 +324,18 @@ def test_MetaCodeList_from_directory():
     }
     exp = MetaCodeList(name="Meta", mapping=mapping)
     assert obs == exp
+
+
+def test_multiple_external_repos():
+    nomenclature_config = NomenclatureConfig.from_file(
+        TEST_DATA_DIR / "nomenclature_configs" / "multiple_repos_per_dimension.yaml"
+    )
+    try:
+        with raises(ValueError, match="Duplicate"):
+            variable_code_list = VariableCodeList.from_directory(
+                "variable",
+                TEST_DATA_DIR / "nomenclature_configs" / "variable",
+                nomenclature_config,
+            )
+    finally:
+        clean_up_external_repos(nomenclature_config.repositories)