diff --git a/model/sync-diff-leaf.h b/model/sync-diff-leaf.h
index a4b6538..1e3143a 100644
--- a/model/sync-diff-leaf.h
+++ b/model/sync-diff-leaf.h
@@ -81,7 +81,9 @@
 std::istream &
 operator >> (std::istream &is, Operation &op);
 
+namespace Error {
 struct SyncDiffLeafOperationParseError : virtual boost::exception, virtual std::exception { };
+} // Error
 
 } // Sync