diff --git a/docs/sdk/PLUGIN_CONTRACT.schema.json b/docs/sdk/PLUGIN_CONTRACT.schema.json
index 70ffc4d33..72f277e72 100644
--- a/docs/sdk/PLUGIN_CONTRACT.schema.json
+++ b/docs/sdk/PLUGIN_CONTRACT.schema.json
@@ -13,7 +13,7 @@
   "$defs": {
     "semver": {
       "type": "string",
-      "pattern": "^[0-9]+\\.[0-9]+\\.[0-9]+([.-][A-Za-z0-9.-]+)?$"
+      "pattern": "^[0-9]+\\.[0-9]+\\.[0-9]+([.-][A-Za-z0-9.-]+)?(?![\\s\\S])"
     },
     "trust_level": {
       "type": "string",
diff --git a/tests/test_plugin_sdk_contract.py b/tests/test_plugin_sdk_contract.py
index b6150bdd8..ec50e7191 100644
--- a/tests/test_plugin_sdk_contract.py
+++ b/tests/test_plugin_sdk_contract.py
@@ -64,6 +64,17 @@ def test_examples_validate_against_contract_schema(example_path: Path) -> None:
     jsonschema.validate(instance=instance, schema=schema)
 
 
+def test_semver_rejects_trailing_newline_on_python_jsonschema() -> None:
+    """Python jsonschema uses re.search; `$` would accept a trailing newline. (#1766)"""
+    semver = _load_schema()["$defs"]["semver"]
+    jsonschema.validate(instance="1.0.0", schema=semver)
+    jsonschema.validate(instance="1.2.3-alpha.1", schema=semver)
+    with pytest.raises(jsonschema.ValidationError):
+        jsonschema.validate(instance="1.0.0\n", schema=semver)
+    with pytest.raises(jsonschema.ValidationError):
+        jsonschema.validate(instance="1.0.0 ", schema=semver)
+
+
 def test_invalid_decision_fails_schema() -> None:
     schema = _load_schema()
     bad = {