diff --git a/adapter/matrix/agent_registry.py b/adapter/matrix/agent_registry.py
index 28bfbed..bac84a9 100644
--- a/adapter/matrix/agent_registry.py
+++ b/adapter/matrix/agent_registry.py
@@ -31,9 +31,9 @@ class AgentRegistry:
 
 def _required_text(entry: Mapping[str, object], key: str) -> str:
     value = entry.get(key)
-    if value is None:
+    if not isinstance(value, str):
         raise AgentRegistryError("each agent entry requires id and label")
-    text = str(value).strip()
+    text = value.strip()
     if not text:
         raise AgentRegistryError("each agent entry requires id and label")
     return text
diff --git a/tests/adapter/matrix/test_agent_registry.py b/tests/adapter/matrix/test_agent_registry.py
index e48a4a5..a918f84 100644
--- a/tests/adapter/matrix/test_agent_registry.py
+++ b/tests/adapter/matrix/test_agent_registry.py
@@ -172,3 +172,28 @@ def test_load_agent_registry_rejects_blank_id_or_label(tmp_path: Path, content:
 
     with pytest.raises(AgentRegistryError, match="each agent entry requires id and label"):
         load_agent_registry(path)
+
+
+@pytest.mark.parametrize(
+    "content",
+    [
+        "agents:\n"
+        "  - id: 123\n"
+        "    label: Analyst\n",
+        "agents:\n"
+        "  - id: agent-1\n"
+        "    label: 456\n",
+        "agents:\n"
+        "  - id: true\n"
+        "    label: Analyst\n",
+        "agents:\n"
+        "  - id: agent-1\n"
+        "    label: false\n",
+    ],
+)
+def test_load_agent_registry_rejects_non_string_id_or_label(tmp_path: Path, content: str):
+    path = tmp_path / "agents.yaml"
+    path.write_text(content, encoding="utf-8")
+
+    with pytest.raises(AgentRegistryError, match="each agent entry requires id and label"):
+        load_agent_registry(path)