diff --git a/sjrpc/core/exceptions.py b/sjrpc/core/exceptions.py
index 5b2aa538eb5d5b05027729fa9117244943a886e2..97e25fb21f30c4d994b8854a843ffb1c04730632 100644
--- a/sjrpc/core/exceptions.py
+++ b/sjrpc/core/exceptions.py
@@ -31,3 +31,11 @@ class NoFreeLabelError(Exception):
     Exception raised when no more free labels are available for protocol
     allocation.
     '''
+
+
+class FallbackModeEnabledError(Exception):
+
+    '''
+    Exception raised when a feature which is not compatible with fallback mode
+    is used.
+    '''
diff --git a/sjrpc/core/rpcconnection.py b/sjrpc/core/rpcconnection.py
index 17f2a115d1a05443695152600076600a84c935c1..2ea587e6e9bea006c76af5066171a761ef80f9cd 100644
--- a/sjrpc/core/rpcconnection.py
+++ b/sjrpc/core/rpcconnection.py
@@ -12,7 +12,8 @@ import socket
 import logging
 
 from sjrpc.core.protocols import Protocol, RpcProtocol, TunnelProtocol
-from sjrpc.core.exceptions import RpcError, NoFreeLabelError
+from sjrpc.core.exceptions import (RpcError, NoFreeLabelError,
+                                   FallbackModeEnabledError)
 
 import pyev
 
@@ -62,6 +63,9 @@ class RpcConnection(object):
         self._sock = sock
         sock.setblocking(False)
 
+        # Initialization requires fallback mode disabled:
+        self.fallback = False
+
         # Get the pyev loop:
         if loop is None:
             self.loop = pyev.default_loop()
@@ -294,6 +298,9 @@ class RpcConnection(object):
         '''
         Register a new protocol for the specified label.
         '''
+        if self.fallback:
+            raise FallbackModeEnabledError('Fallback mode is not compatible '
+                                           'with protocols')
         if label is None:
             for label in xrange(0, RpcConnection.MAX_LABEL):
                 if label not in self._protocols:
@@ -312,6 +319,9 @@ class RpcConnection(object):
         Unregister the specified protocol label for this connection.
         '''
 
+        if self.fallback:
+            raise FallbackModeEnabledError('Fallback mode is not compatible '
+                                           'with protocols')
         if label in self._protocols and label != 0:
             del self._protocols[label]
         else: