diff --git a/tools/import-normalizer/persons.py b/tools/import-normalizer/persons.py
index b9106245..41f66458 100644
--- a/tools/import-normalizer/persons.py
+++ b/tools/import-normalizer/persons.py
@@ -197,6 +197,22 @@ def classify_name(raw: str, given_names: set[str]) -> NameClass:
 # register; if they surface in review, lower-priority than the real prose entries.
 
 
+def build_given_names(register: list[Person], extra: set[str]) -> set[str]:
+    """Set of normalized given names from the register (first + extra given) plus a supplement.
+
+    Used by classify_name to tell a two-given-name pair (two people) from a first+surname.
+    """
+    names: set[str] = set()
+    for p in register:
+        if p.first_name:
+            names.add(_norm(p.first_name))
+        for g in p.extra_given_names:
+            names.add(_norm(g))
+    for e in extra:
+        names.add(_norm(e))
+    return names
+
+
 class AliasIndex:
     def __init__(self, people: list[Person]):
         self._by_alias: dict[str, str] = {}
diff --git a/tools/import-normalizer/tests/test_persons.py b/tools/import-normalizer/tests/test_persons.py
index 53ed62df..5d26ecfa 100644
--- a/tools/import-normalizer/tests/test_persons.py
+++ b/tools/import-normalizer/tests/test_persons.py
@@ -119,3 +119,14 @@ def test_classify_resolvable_single_person():
     # first + surname (surname not a given name) -> one real person, NOT ambiguous
     assert persons.classify_name("Mieze Schefold", GIVEN) is NameClass.RESOLVABLE
     assert persons.classify_name("Adolf Butenandt", GIVEN) is NameClass.RESOLVABLE
+
+def test_build_given_names():
+    people = persons.parse_register([
+        {"last_name": "de Gruyter", "first_name": "Eugenie"},
+        {"last_name": "Cram", "first_name": "Charlotte,Meta"},  # comma -> primary + extra given
+    ])
+    g = persons.build_given_names(people, {"Anita"})
+    assert "eugenie" in g
+    assert "charlotte" in g and "meta" in g   # primary + extra given names
+    assert "anita" in g                        # from the extra set, normalized
+    assert "schefold" not in g