How to resolve undefined symbol referenced from my plugin for ray sensor?

I've created a Gazebo Plugin that inherits from the RayPlugin type. class CustomPlugin : public RayPlugin It compiles just fine (using Gazebo 9), but when I launch Gazebo I get the following error. [Err] [Plugin.hh:180] Failed to load plugin {path_to_plugin}/libcustom_plugin.so: {path_to_plugin}/libcustom_plugin.so: undefined symbol: _ZTIN6gazebo9RayPluginE I am referencing it in my model file like this: In my CMakeLists.txt, I am linking like this: add_library(custom_plugin SHARED plugins/custom_plugin.cpp) target_link_libraries(custom_plugin ${GAZEBO_LIBRARIES} ${IGNITION-MSGS_LIBRARIES}) I've done two things to ensure that the GAZEBO_PLUGIN_PATH is set correctly. First, I've used the tag in package.xml. Secondly, I've manually set the variable to reference both the native Gazebo plugins and the lib folder. export GAZEBO_PLUGIN_PATH=/usr/lib/x86_64-linux-gnu/gazebo-9/plugins:{path_to_ros_package}/devel/lib I've verified that /usr/lib/x86_64-linux-gnu/gazebo-9/plugins contains libRayPlugin.so. Neither of these two works. I am at a loss. Any thoughts?