diff --git a/DDCore/CMakeLists.txt b/DDCore/CMakeLists.txt
index fc752dc5a337fd104b2b67b0f9c89ee6b7f1006c..e8bc4a493915a8b88828d32e4c393c9e04d1a7f4 100644
--- a/DDCore/CMakeLists.txt
+++ b/DDCore/CMakeLists.txt
@@ -42,7 +42,8 @@ dd4hep_add_package_library ( DDParsers
 
 #---Generate DDCore Library-------------------------------------------------------
 dd4hep_add_package_library ( DDCore
-  SOURCES        src/*.cpp src/XML/*.cpp src/JSON/*.cpp
+  SOURCES        src/*.cpp src/XML/*.cpp
+  OPTIONAL       [BOOST SOURCES src/JSON/*.cpp]
   GENERATED      G__DD4hep.cxx 
   INCLUDE_DIRS   ${GaudiPluginService_INCLUDE_DIRS}
   LINK_LIBRARIES DDParsers ${GaudiPluginService_LIBRARIES}