diff --git a/emulators/nestopia.yml b/emulators/nestopia.yml
index afd53bb8..1d596c74 100644
--- a/emulators/nestopia.yml
+++ b/emulators/nestopia.yml
@@ -40,10 +40,12 @@ files:
     description: "FDS BIOS ROM"
     required: true
     size: 8192
+    crc32: ["5e607dcf", "4df24a6c"]
     validation: [crc32]
+    on_mismatch: warn
     md5: "ca30b50f880eb660a320674ed365ef7a"
     sha1: "57fe1bdee955bb48d357e463ccbf129496930b62"
-    source_ref: "libretro/libretro.cpp:2169-2197 (FDS load), source/core/NstFds.cpp:57-127 (Bios class, CRC32 validation)"
+    source_ref: "libretro/libretro.cpp:2169-2197 (FDS load), source/core/NstFds.cpp:57-127 (Bios class, CRC32 logged), source/core/api/NstApiFds.cpp:101-150 (iNES header skipped)"
     note: "Mapped at 0xE000-0xFFFF (8 KB). retro_load_game returns false if missing when loading .fds files. CRC32 checked: Famicom 0x5E607DCF, Twin Famicom 0x4DF24A6C."
 
   # --- NES game database (optional, overrides baked-in copy) ---
diff --git a/tests/test_profile_checks.py b/tests/test_profile_checks.py
index 44dd125c..7b3d1881 100644
--- a/tests/test_profile_checks.py
+++ b/tests/test_profile_checks.py
@@ -291,5 +291,15 @@ class MgbaGameBoyBootRoms(_Probe):
                 self.assertFalse(self.accepts("mgba", name, b"\0" * size))
 
 
+class NestopiaFdsBios(_Probe):
+    """Fds::Bios logs "warning, unknown BIOS ROM!" for a CRC32 other than the
+    Famicom and Twin Famicom ones and uses the ROM (source/core/NstFds.cpp
+    57-127 at b9fdc9c). The profile declared the check with no value."""
+
+    def test_an_unknown_bios_only_warns(self):
+        self.assertTrue(self.accepts("nestopia", "disksys.rom", b"\0" * 8192))
+        self.assertFalse(self.accepts("nestopia", "disksys.rom", b"\0" * 8192, strict=True))
+
+
 if __name__ == "__main__":
     unittest.main()