diff --git a/tools/CMakeLists.txt b/tools/CMakeLists.txt
index 4a398d03a..64efe0db9 100644
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -1,6 +1,7 @@
 
 add_subdirectory(caffe)
 add_subdirectory(mxnet)
+add_subdirectory(onnx)
 
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../src)
 include_directories(${CMAKE_CURRENT_BINARY_DIR}/../src)
diff --git a/tools/caffe/CMakeLists.txt b/tools/caffe/CMakeLists.txt
index a6e035518..4d549ad23 100644
--- a/tools/caffe/CMakeLists.txt
+++ b/tools/caffe/CMakeLists.txt
@@ -8,6 +8,5 @@ if(PROTOBUF_FOUND)
     add_executable(caffe2ncnn caffe2ncnn.cpp ${CAFFE_PROTO_SRCS} ${CAFFE_PROTO_HDRS})
     target_link_libraries(caffe2ncnn ${PROTOBUF_LIBRARIES})
 else()
-    MESSAGE(WARNING "Protobuf not found, caffe model convert tools won't build")
+    message(WARNING "Protobuf not found, caffe model convert tool won't be built")
 endif()
-
diff --git a/tools/onnx/CMakeLists.txt b/tools/onnx/CMakeLists.txt
index 8ca98d8b5..5fdec3ecc 100644
--- a/tools/onnx/CMakeLists.txt
+++ b/tools/onnx/CMakeLists.txt
@@ -1,11 +1,12 @@
 
-find_package(Protobuf REQUIRED)
-
-include_directories(${PROTOBUF_INCLUDE_DIR})
-
-include_directories(${CMAKE_CURRENT_BINARY_DIR})
-protobuf_generate_cpp(ONNX_PROTO_SRCS ONNX_PROTO_HDRS onnx.proto)
-
-add_executable(onnx2ncnn onnx2ncnn.cpp ${ONNX_PROTO_SRCS} ${ONNX_PROTO_HDRS})
-
-target_link_libraries(onnx2ncnn ${PROTOBUF_LIBRARIES})
+find_package(Protobuf)
+
+if(PROTOBUF_FOUND)
+    include_directories(${PROTOBUF_INCLUDE_DIR})
+    include_directories(${CMAKE_CURRENT_BINARY_DIR})
+    protobuf_generate_cpp(ONNX_PROTO_SRCS ONNX_PROTO_HDRS onnx.proto)
+    add_executable(onnx2ncnn onnx2ncnn.cpp ${ONNX_PROTO_SRCS} ${ONNX_PROTO_HDRS})
+    target_link_libraries(onnx2ncnn ${PROTOBUF_LIBRARIES})
+else()
+    message(WARNING "Protobuf not found, onnx model convert tool won't be built")
+endif()