diff --git a/fints/client.py b/fints/client.py
index 213972a..61ab21c 100644
--- a/fints/client.py
+++ b/fints/client.py
@@ -1305,6 +1305,9 @@ def fetch_tan_mechanisms(self):
         else:
             self.set_tan_mechanism('999')
             self._ensure_system_id()
+        # Bootstrap phase (anonymous dialog with sf=999) is complete.
+        # Reset so that errors in subsequent authenticated dialogs are properly raised.
+        self._bootstrap_mode = False
         if self.get_current_tan_mechanism():
             # We already got a reply through _ensure_system_id
             return self.get_current_tan_mechanism()
diff --git a/fints/security.py b/fints/security.py
index e9f14e1..bab41ac 100644
--- a/fints/security.py
+++ b/fints/security.py
@@ -99,13 +99,14 @@ def __init__(self, pin):
         self.pin = pin
         self.pending_signature = None
         self.security_function = None
+        self.security_method_version = 1
 
     def sign_prepare(self, message: FinTSMessage):
         _now = datetime.datetime.now()
         rand = random.SystemRandom()
 
         self.pending_signature = HNSHK4(
-            security_profile=SecurityProfile(SecurityMethod.PIN, 1),
+            security_profile=SecurityProfile(SecurityMethod.PIN, self.security_method_version),
             security_function=self.security_function,
             security_reference=rand.randint(1000000, 9999999),
             security_application_area=SecurityApplicationArea.SHM,
@@ -178,6 +179,7 @@ def __init__(self, client, security_function, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.client = client
         self.security_function = security_function
+        self.security_method_version = 2
 
     def _get_tan(self):
         retval = self.client._pending_tan