diff --git a/emulators/beetle_gba.yml b/emulators/beetle_gba.yml
index 07c7e9c0..84c23e42 100644
--- a/emulators/beetle_gba.yml
+++ b/emulators/beetle_gba.yml
@@ -1,14 +1,22 @@
 # Beetle GBA (Mednafen) — Game Boy Advance (libretro)
 # ref: beetle-gba-libretro/mednafen/gba, docs.libretro.com/library/beetle_gba
-# Same BIOS as mGBA/VBA-M. Optional, no HLE fallback documented.
+# Same BIOS as mGBA/VBA-M. Read only with the gba_hle core option disabled.
 emulator: Beetle GBA (Mednafen)
 type: libretro
 cores: [mednafen_gba]
 source: "https://github.com/libretro/beetle-gba-libretro"
+source_commit: "b158166237b17253188cfdbe73a8a0b9fe4b3a8c"
 systems:
   - nintendo-gba
 files:
   - name: gba_bios.bin
     system: nintendo-gba
     required: false
-    md5: a860e8c0b6d573d191e4ec7db1b1e4f6
+    hle_fallback: true
+    size: 16384
+    validation: [size]
+    source_ref: "mednafen/gba/GBA.cpp:2639-2673, mednafen/settings.cpp:81-82, libretro.cpp:223-230"
+    note: >
+      Read only when the gba_hle core option is disabled; it is enabled by
+      default and the core then uses its built-in HLE BIOS. A file of any size
+      other than 16384 bytes is ignored and the core falls back to HLE.
diff --git a/tests/test_profile_checks.py b/tests/test_profile_checks.py
index 7cb54661..31239214 100644
--- a/tests/test_profile_checks.py
+++ b/tests/test_profile_checks.py
@@ -99,5 +99,17 @@ class BeetleLynxBootRom(_Probe):
         self.assertTrue(self.accepts("beetle_lynx", "lynxboot.img", b"\0" * 1024))
 
 
+class BeetleGbaBios(_Probe):
+    """CPUInit copies the BIOS only when it is exactly 0x4000 bytes and
+    otherwise falls back to HLE (mednafen/gba/GBA.cpp:2639-2673 at
+    b158166)."""
+
+    def test_only_16k_is_used(self):
+        self.assertTrue(self.accepts("beetle_gba", "gba_bios.bin", b"\0" * 16384))
+        for size in (1000, 32768):
+            with self.subTest(size=size):
+                self.assertFalse(self.accepts("beetle_gba", "gba_bios.bin", b"\0" * size))
+
+
 if __name__ == "__main__":
     unittest.main()