diff --git a/fwk/_src/CMakeLists.txt b/fwk/_src/CMakeLists.txt
index a1e220fd29675d98f3d7a279044ef7bc3b6d74a3..fa26e7c3cce7349259a4e954a2738d4f5fccb86a 100644
--- a/fwk/_src/CMakeLists.txt
+++ b/fwk/_src/CMakeLists.txt
@@ -20,7 +20,7 @@ FILE(GLOB SRCS *.h *.cpp *.inl *.swg)
 FILE(GLOB ISRCS *.i)
 
 SET_SOURCE_FILES_PROPERTIES(${ISRCS} PROPERTIES CPLUSPLUS ON)
-SET(CMAKE_SWIG_FLAGS "-interface" "_fwkw") # avoids "import _module_d" with MSVC/Debug
+SET(CMAKE_SWIG_FLAGS ${CMAKE_SWIG_FLAGS} "-interface" "_fwkw") # avoids "import _module_d" with MSVC/Debug
 SWIG_ADD_LIBRARY(fwkw LANGUAGE python SOURCES ${ISRCS} ${SRCS})
 SET_PROPERTY(TARGET fwkw PROPERTY SWIG_USE_TARGET_INCLUDE_DIRECTORIES ON)
 MACRO_DebugPostfix(fwkw)
diff --git a/tbox/_src/CMakeLists.txt b/tbox/_src/CMakeLists.txt
index 02151e8e9b65f760ffb6ce57b29fea66cb388862..9e309715d7fd92b4cd209b1afd2e37159a8b2435 100644
--- a/tbox/_src/CMakeLists.txt
+++ b/tbox/_src/CMakeLists.txt
@@ -20,7 +20,7 @@ FILE(GLOB SRCS *.h *.cpp *.inl *.swg)
 FILE(GLOB ISRCS *.i)
 
 SET_SOURCE_FILES_PROPERTIES(${ISRCS} PROPERTIES CPLUSPLUS ON)
-SET(CMAKE_SWIG_FLAGS "-interface" "_tboxw") # avoids "import _module_d" with MSVC/Debug
+SET(CMAKE_SWIG_FLAGS ${CMAKE_SWIG_FLAGS} "-interface" "_tboxw") # avoids "import _module_d" with MSVC/Debug
 SWIG_ADD_LIBRARY(tboxw LANGUAGE python SOURCES ${ISRCS} ${SRCS})
 SET_PROPERTY(TARGET tboxw PROPERTY SWIG_USE_TARGET_INCLUDE_DIRECTORIES ON)
 MACRO_DebugPostfix(tboxw)
diff --git a/tboxVtk/_src/CMakeLists.txt b/tboxVtk/_src/CMakeLists.txt
index c0f894bba572447026d8d4788e018a614ceb105c..0011635748f147cd815dc45199cc4ad1a955ad05 100644
--- a/tboxVtk/_src/CMakeLists.txt
+++ b/tboxVtk/_src/CMakeLists.txt
@@ -20,7 +20,7 @@ FILE(GLOB SRCS *.h *.cpp *.inl *.swg)
 FILE(GLOB ISRCS *.i)
 
 SET_SOURCE_FILES_PROPERTIES(${ISRCS} PROPERTIES CPLUSPLUS ON)
-SET(CMAKE_SWIG_FLAGS "-interface" "_tboxVtkw") # avoids "import _module_d" with MSVC/Debug
+SET(CMAKE_SWIG_FLAGS ${CMAKE_SWIG_FLAGS} "-interface" "_tboxVtkw") # avoids "import _module_d" with MSVC/Debug
 SWIG_ADD_LIBRARY(tboxVtkw LANGUAGE python SOURCES ${ISRCS} ${SRCS})
 SET_PROPERTY(TARGET tboxVtkw PROPERTY SWIG_USE_TARGET_INCLUDE_DIRECTORIES ON)
 MACRO_DebugPostfix(tboxVtkw)