diff --git a/scripts/validate_schemas.py b/scripts/validate_schemas.py
index 055495866..9ec74b88e 100644
--- a/scripts/validate_schemas.py
+++ b/scripts/validate_schemas.py
@@ -714,7 +714,13 @@ def _semantic_install_checks(path: Path, manifest: dict) -> list[str]:
     destinations = [(entry.get("root"), entry.get("dest")) for entry in files]
     if len(destinations) != len(set(destinations)):
         out.append(f"{path.relative_to(ROOT)}: duplicate destinations")
-    omitted_destinations = [(entry.get("root"), entry.get("dest")) for entry in omitted]
+    # root: emulator is each core's own folder: mame2015 and mame2016 read
+    # 3dobios.zip in two places, one omission each, named by its cores.
+    omitted_destinations = [
+        (entry.get("root"), entry.get("dest"),
+         tuple(entry.get("cores") or ()) if entry.get("root") == "emulator" else ())
+        for entry in omitted
+    ]
     if len(omitted_destinations) != len(set(omitted_destinations)):
         out.append(f"{path.relative_to(ROOT)}: duplicate omitted destinations")
     overlap = set(destinations) & set(omitted_destinations)
diff --git a/tests/test_schema_semantic_gate.py b/tests/test_schema_semantic_gate.py
index 5d6fd9983..41a04dd50 100644
--- a/tests/test_schema_semantic_gate.py
+++ b/tests/test_schema_semantic_gate.py
@@ -95,6 +95,24 @@ class SemanticManifestValidation(unittest.TestCase):
         self.assertEqual(len(errors), 1)
         self.assertIn("total_files does not equal len(files)", errors[0])
 
+    def test_an_emulator_folder_omission_is_keyed_by_its_cores(self):
+        """mame2015 and mame2016 read 3dobios.zip each in its own folder:
+        two omissions, two places. The same core twice is one place."""
+        path = REPO_ROOT / "install" / "synthetic.json"
+
+        def omission(core: str) -> dict:
+            return {"dest": "3dobios.zip", "root": "emulator", "cores": [core]}
+
+        def errors(omitted: list[dict]) -> list[str]:
+            manifest = {"files": [], "total_files": 0, "total_size": 0,
+                        "omitted_files": omitted, "total_omitted": len(omitted)}
+            return [e for e in validate_schemas._semantic_install_checks(path, manifest)
+                    if "omitted destinations" in e]
+
+        self.assertEqual(errors([omission("mame2015"), omission("mame2016")]), [])
+        self.assertEqual(len(errors([omission("mame2015"), omission("mame2015")])), 1)
+        self.assertEqual(len(errors([{"dest": "a.bin"}, {"dest": "a.bin"}])), 1)
+
 
 try:
     import jsonschema