diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0db49c77f73..0de20e5ed8e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -103,11 +103,6 @@ else()
   set(ONNX_NAMESPACE "onnx")
   set(MY_ONNX_NAMESPACE "-DONNX_NAMESPACE=onnx")
 endif()
-add_definitions(${MY_ONNX_NAMESPACE})
-
-if(ONNX_ML)
-  add_definitions("-DONNX_ML=1")
-endif()
 
 # function(RELATIVE_PROTOBUF_GENERATE_CPP SRCS HDRS ROOT_DIR) from https://githu
 # b.com/tensorflow/tensorflow/blob/d2c3b873c6f8ff999a2e4ee707a84ff00d9c15a5/tens
@@ -276,11 +271,19 @@ if(TARGET protobuf::libprotobuf)
 else()
   target_link_libraries(onnx_proto PUBLIC ${PROTOBUF_LIBRARIES})
 endif()
+target_compile_definitions(onnx_proto PUBLIC ${MY_ONNX_NAMESPACE})
 
 add_library(onnx ${onnx_src})
 target_include_directories(onnx
                            PUBLIC ${ONNX_ROOT} "${CMAKE_CURRENT_BINARY_DIR}")
 target_link_libraries(onnx PUBLIC onnx_proto)
+# interface compile options of onnx_proto will also take effect here, but I think setting it explicitly is better.
+target_compile_definitions(onnx PUBLIC ${MY_ONNX_NAMESPACE})
+
+if(ONNX_ML)
+  target_compile_definitions(onnx_proto PUBLIC ONNX_ML=1)
+  target_compile_definitions(onnx PUBLIC ONNX_ML=1)
+endif()
 
 if(BUILD_ONNX_PYTHON)
   if("${PY_EXT_SUFFIX}" STREQUAL "")
@@ -298,6 +301,8 @@ if(BUILD_ONNX_PYTHON)
   set_target_properties(onnx_cpp2py_export PROPERTIES SUFFIX ${PY_EXT_SUFFIX})
   set_target_properties(onnx_cpp2py_export
                         PROPERTIES LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
+  # Setting compile flags about namespace explicitly
+  target_compile_definitions(onnx_cpp2py_export PUBLIC ${MY_ONNX_NAMESPACE})
   target_include_directories(onnx_cpp2py_export
                              PRIVATE "${ONNX_ROOT}"
                                      "${CMAKE_CURRENT_BINARY_DIR}"
@@ -372,6 +377,9 @@ if(BUILD_ONNX_PYTHON)
                                    ${EXTRA_FLAGS})
     target_compile_options(onnx_cpp2py_export PRIVATE /MT)
   endif()
+  if (ONNX_ML)
+    target_compile_definitions(onnx_cpp2py_export PUBLIC ONNX_ML=1)
+  endif()
 endif()
 
 if(ONNX_BUILD_BENCHMARKS)