diff --git a/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp b/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
index adc4d73..02918d2 100644
--- a/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
+++ b/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
@@ -1769,9 +1769,8 @@ void CSteamNetworkingSockets::InternalQueueCallback( int nCallback, int cbCallba
 		AssertMsg( false, "Callback doesn't fit!" );
 		return;
 	}
-	AssertMsg( len( m_vecPendingCallbacks ) < 100, "Callbacks backing up and not being checked.  Need to check them more frequently!" );
-
 	m_mutexPendingCallbacks.lock();
+	AssertMsg( len( m_vecPendingCallbacks ) < 100, "Callbacks backing up and not being checked.  Need to check them more frequently!" );
 	QueuedCallback &q = *push_back_get_ptr( m_vecPendingCallbacks );
 	q.nCallback = nCallback;
 	q.fnCallback = fnRegisteredFunctionPtr;