diff --git a/scripts/packextras.py b/scripts/packextras.py
index 23d13e4b1..900c21658 100644
--- a/scripts/packextras.py
+++ b/scripts/packextras.py
@@ -253,11 +253,27 @@ class ExtraResolver:
         self.validation_index = validation_index
         self.validation_owners = validation_owners
         self.offline = offline
+        # Each profile's entries by slot, built on first use: every extra
+        # scanned its whole profile, 33 million entries in one verify --all.
+        self._slots: dict[str, dict[tuple[str, str], list[dict]]] = {}
+
+    def alternatives(self, fe: dict) -> list[dict]:
+        """The versions the extra's own profile accepts at its slot, as
+        validation.extra_alternatives finds them."""
+        from validation import slot_index
+
+        key = fe.get("source_profile") or ""
+        index = self._slots.get(key)
+        if index is None:
+            profile = (self.profiles or {}).get(key, {})
+            index = self._slots[key] = slot_index(profile.get("files") or [])
+        name = fe.get("source_name") or fe.get("name", "")
+        return index.get((name, fe.get("source_path") or name), [])
 
     def resolve(self, fe: dict, dest: str) -> tuple[str | None, str, str]:
         """(local copy or None, resolver status, the core's disagreement)."""
         from packresolve import resolve_file
-        from validation import core_size_refusal, extra_alternatives, validated_choice
+        from validation import core_size_refusal, validated_choice
 
         local_path, status = resolve_file(
             fe, self.db, self.bios_dir, self.zip_contents,
@@ -272,9 +288,7 @@ class ExtraResolver:
         )
         # The platform never reads the bytes, the core does: a copy it turns
         # away by its own size check is not its file, on any platform.
-        if core_size_refusal(
-            fe, local_path, extra_alternatives(fe, self.profiles)
-        ):
+        if core_size_refusal(fe, local_path, self.alternatives(fe)):
             return None, "not_found", ""
         return local_path, status, disagreement
 
diff --git a/scripts/validation.py b/scripts/validation.py
index 7a8e9dad2..300e36d05 100644
--- a/scripts/validation.py
+++ b/scripts/validation.py
@@ -1004,6 +1004,17 @@ def same_slot_entries(files: list, name: str, path: str) -> list[dict]:
     ]
 
 
+def slot_index(files: list) -> dict[tuple[str, str], list[dict]]:
+    """A profile's entries keyed by (name, path), as same_slot_entries
+    matches them: one pass, then one lookup per extra."""
+    index: dict[tuple[str, str], list[dict]] = {}
+    for entry in files or []:
+        if isinstance(entry, dict):
+            name = entry.get("name")
+            index.setdefault((name, entry.get("path") or name), []).append(entry)
+    return index
+
+
 def extra_alternatives(fe: dict, profiles: Mapping | None) -> list[dict]:
     """The versions the extra's own profile accepts at the extra's slot."""
     if not profiles:
diff --git a/tests/test_validated_choice.py b/tests/test_validated_choice.py
index 3ad102bd3..ca7198b3c 100644
--- a/tests/test_validated_choice.py
+++ b/tests/test_validated_choice.py
@@ -296,5 +296,34 @@ class AWarningRejectsNothing(unittest.TestCase):
             short, _good, _db, index = self._setup(tmp, held_good=False)
             self.assertIsNone(check_file_validation(str(short), "OS12.rom", index, tmp))
 
+
+class AlternativesAreLookedUpBySlot(unittest.TestCase):
+    """Each extra scanned its whole profile for the versions of its slot:
+    33 million entries visited in one verify --all."""
+
+    def test_same_answer_one_pass_per_profile(self):
+        from unittest import mock
+
+        import packextras
+        import validation
+
+        files = [{"name": "DUKE3D.GRP", "size": n} for n in (1, 2)] + [
+            {"name": "a.bin", "path": "dir/a.bin"}, {"name": "a.bin"}, "not an entry",
+        ]
+        profiles = {"raze": {"files": files}}
+        resolver = packextras.ExtraResolver({}, "bios", None, None, {}, None, profiles=profiles)
+        extras = [
+            {"source_profile": "raze", "name": "DUKE3D.GRP"},
+            {"source_profile": "raze", "name": "a.bin", "source_path": "dir/a.bin"},
+            {"source_profile": "raze", "source_name": "a.bin", "name": "renamed"},
+            {"source_profile": "other", "name": "a.bin"},
+        ]
+        with mock.patch.object(validation, "slot_index", side_effect=validation.slot_index) as built:
+            for fe in extras:
+                self.assertEqual(resolver.alternatives(fe),
+                                 validation.extra_alternatives(fe, profiles))
+        self.assertEqual(built.call_count, 2)
+
+
 if __name__ == "__main__":
     unittest.main()