diff --git a/scripts/generate_pack.py b/scripts/generate_pack.py
index 9e2a2684..28961749 100644
--- a/scripts/generate_pack.py
+++ b/scripts/generate_pack.py
@@ -490,7 +490,8 @@ def _select_variants(
             for sys_id, members in region_groups.items()
         }
         slot_drops, slot_undecidable = slot_mod.resolve_slot_drops(
-            slot_groups, slot_mod.build_slot_index(emu_profiles or {})
+            slot_groups,
+            slot_mod.platform_slot_index(config, emu_profiles or {}, target_cores),
         )
         region_drops = region_drops | slot_drops
         if slot_undecidable:
diff --git a/scripts/slot.py b/scripts/slot.py
index bae36afa..f08049ad 100644
--- a/scripts/slot.py
+++ b/scripts/slot.py
@@ -30,6 +30,21 @@ from __future__ import annotations
 BIOS_CATEGORY = "bios"
 
 
+def platform_slot_index(
+    config: dict, profiles: dict, target_cores: set[str] | None = None
+) -> dict[str, dict]:
+    """The slot index of the emulators a platform runs, nothing else.
+
+    Built over every profile, DuckStation, ePSXe and Rustation ranked the
+    PlayStation BIOS of RomM, whose cores rank none of them, and
+    `--one-per-slot` dropped four images RomM declares.
+    """
+    from common import resolve_platform_cores  # noqa: PLC0415
+
+    cores = resolve_platform_cores(config, profiles, target_cores=target_cores)
+    return build_slot_index({n: profiles[n] for n in cores if n in profiles})
+
+
 def build_slot_index(profiles: dict) -> dict[str, dict]:
     """Map a file key to its slot metadata, keyed by path then name."""
     index: dict[str, dict] = {}
diff --git a/tests/test_region_platform_index.py b/tests/test_region_platform_index.py
index a91bf96f..4d2be7cb 100644
--- a/tests/test_region_platform_index.py
+++ b/tests/test_region_platform_index.py
@@ -40,5 +40,34 @@ class OnlyThePlatformsCores(unittest.TestCase):
             self.assertIn("platform_region_index(", source, module)
 
 
+
+class OnlyThePlatformsCoresRankASlot(unittest.TestCase):
+    """RomM runs beetle_psx and pcsx_rearmed, which rank no PlayStation
+    BIOS; DuckStation's ranks dropped four images RomM declares."""
+
+    PROFILES = {
+        "beetle_psx": {"emulator": "Beetle", "type": "libretro",
+                       "systems": ["sony-playstation"],
+                       "files": [{"name": "scph100.bin"}, {"name": "scph5501.bin"}]},
+        "duckstation": {"emulator": "DuckStation", "type": "standalone",
+                        "systems": ["sony-playstation"],
+                        "files": [{"name": "scph100.bin", "priority": 10},
+                                  {"name": "scph5501.bin", "priority": 5}]},
+    }
+
+    def test_a_foreign_rank_orders_nothing(self):
+        import slot as slot_mod  # noqa: PLC0415
+
+        config = {"cores": ["beetle_psx"], "systems": {"sony-playstation": {"files": []}}}
+        index = slot_mod.platform_slot_index(config, self.PROFILES)
+        self.assertIsNone(index["scph100.bin"]["rank"])
+        self.assertEqual(slot_mod.build_slot_index(self.PROFILES)["scph100.bin"]["rank"], 10)
+
+    def test_the_pack_reads_it(self):
+        source = (REPO_ROOT / "scripts" / "generate_pack.py").read_text(encoding="utf-8")
+        self.assertNotIn("build_slot_index(", source)
+        self.assertIn("platform_slot_index(", source)
+
+
 if __name__ == "__main__":
     unittest.main()