diff --git a/xtest/otdfctl.py b/xtest/otdfctl.py
index b937aa58c..9ab99d478 100644
--- a/xtest/otdfctl.py
+++ b/xtest/otdfctl.py
@@ -312,7 +312,10 @@ def kas_registry_create_key(
         # Handle race condition: if key already exists, return the existing one
         if process.returncode != 0:
             err_str = (err.decode() if err else "") + (out.decode() if out else "")
-            if "Invalid key parameters: invalid algorithm" in err_str:
+            if (
+                "Invalid key parameters: invalid algorithm" in err_str
+                or "key_algorithm_defined" in err_str
+            ):
                 raise InvalidAlgorithm(
                     f"Algorithm not supported by platform: {err_str}"
                 )
diff --git a/xtest/tdfs.py b/xtest/tdfs.py
index 4501604c6..2dcd28752 100644
--- a/xtest/tdfs.py
+++ b/xtest/tdfs.py
@@ -136,8 +136,10 @@ def __init__(self, **kwargs: dict[str, Any]):
         if self.semver >= (0, 13, 0):
             self.features.add("mechanism-ec-curves-384-521")
 
-        # X-Wing hybrid PQ/T KEM support (ML-KEM-768 + X25519)
-        if self.semver >= (0, 14, 0):
+        # X-Wing / secp+ML-KEM hybrid PQ/T KEM support.
+        # Key management API for hpqt:* algorithms landed after service/v0.15.0;
+        # v0.15.0 rejects them with a key_algorithm validation error.
+        if self.semver >= (0, 16, 0):
             self.features.add("mechanism-xwing")
             self.features.add("mechanism-secpmlkem")