diff --git a/model/sync-state.h b/model/sync-state.h
index 26ea5f4..7c0b98e 100644
--- a/model/sync-state.h
+++ b/model/sync-state.h
@@ -88,10 +88,12 @@
 std::istream &
 operator >> (std::istream &in, State &state);
 
+namespace Error {
 /**
  * @brief Will be thrown when XML cannot be properly decoded to State
  */
 struct SyncXmlDecodingFailure : virtual boost::exception, virtual std::exception { };
+}
 
 } // Sync