diff --git a/litellm/proxy/a2a/agent_card.py b/litellm/proxy/a2a/agent_card.py
index 129ad8f0a96..29a689a32de 100644
--- a/litellm/proxy/a2a/agent_card.py
+++ b/litellm/proxy/a2a/agent_card.py
@@ -7,6 +7,7 @@ the base; specific fields are replaced so all traffic flows through the proxy
 and uses LiteLLM auth.
 """
 
+import re
 from copy import deepcopy
 from typing import Any, Dict, List, Literal, Mapping
 
@@ -20,16 +21,25 @@ SUPPORTED_A2A_PROTOCOL_VERSIONS: tuple[SupportedA2AVersion, ...] = ("0.3", "1.0"
 LITELLM_A2A_PROTOCOL_VERSION = "1.0"
 
 
+_PROTOCOL_VERSION_PATTERN = re.compile(
+    r"^(\d+\.\d+)(?:\.\d+(?:-[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*)?(?:\+[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*)?)?$"
+)
+
+
 def normalize_protocol_version(version: object) -> SupportedA2AVersion | None:
     """Map a raw ``protocolVersion`` value to the supported canonical major.minor version.
 
-    Semver strings the A2A spec and Google a2a-sdk emit (e.g. ``"0.3.0"``, ``"1.0.1"``)
-    canonicalize to their major.minor (``"0.3"``, ``"1.0"``). Anything outside the
-    supported set, including non-strings, yields ``None``.
+    Accepts the bare major.minor convention of the 1.0 spec (``"0.3"``, ``"1.0"``) and the
+    full semver forms older SDKs emit (``"0.3.0"``, ``"1.0.1"``, including prerelease and
+    build suffixes like ``"0.3.0-rc1"``). Malformed strings, versions outside the
+    supported set, and non-strings yield ``None``.
     """
     if not isinstance(version, str):
         return None
-    major_minor = ".".join(version.split(".")[:2])
+    match = _PROTOCOL_VERSION_PATTERN.match(version)
+    if match is None:
+        return None
+    major_minor = match.group(1)
     return next((supported for supported in SUPPORTED_A2A_PROTOCOL_VERSIONS if supported == major_minor), None)
 
 
diff --git a/tests/test_litellm/proxy/a2a/test_agent_card.py b/tests/test_litellm/proxy/a2a/test_agent_card.py
index 32e211b45be..dfa848e335e 100644
--- a/tests/test_litellm/proxy/a2a/test_agent_card.py
+++ b/tests/test_litellm/proxy/a2a/test_agent_card.py
@@ -219,9 +219,16 @@ def test_strips_additional_interfaces_to_prevent_backend_url_leak():
         ("1.0", "1.0"),
         ("1.0.0", "1.0"),
         ("1.0.1", "1.0"),
+        ("0.3.0-rc1", "0.3"),
+        ("1.0.0-rc.1+build.5", "1.0"),
         ("0.2.6", None),
         ("2.0", None),
         ("0.30", None),
+        ("0.3.garbage", None),
+        ("0.3.", None),
+        ("1.0.not-semver", None),
+        ("0.3.0.0", None),
+        ("0.3-rc1", None),
         ("garbage", None),
         ("", None),
         (None, None),
diff --git a/tests/test_litellm/proxy/agent_endpoints/test_endpoints.py b/tests/test_litellm/proxy/agent_endpoints/test_endpoints.py
index d4228f799d5..bcd3333baf9 100644
--- a/tests/test_litellm/proxy/agent_endpoints/test_endpoints.py
+++ b/tests/test_litellm/proxy/agent_endpoints/test_endpoints.py
@@ -580,6 +580,12 @@ class TestAgentProtocolVersionValidation:
         assert "Unsupported protocolVersion '0.2.6'" in resp.json()["detail"]
         self.mock_registry.add_agent_to_db.assert_not_awaited()
 
+    def test_malformed_protocol_version_is_rejected(self):
+        resp = self._create_agent_with_protocol_version("0.3.garbage")
+        assert resp.status_code == 400
+        assert "Unsupported protocolVersion '0.3.garbage'" in resp.json()["detail"]
+        self.mock_registry.add_agent_to_db.assert_not_awaited()
+
 
 class TestCheckAgentManagementPermission:
     """Unit tests for the _check_agent_management_permission helper."""