Including generated headers from devel/include space

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Hello,

I have a package, let's call it gen. It is built under catkin kinetic and I can see the gen.h in workspace/devel/include.
In another package, let's call it toCompile. The code is unable to find gen.h

workspace/src/toCompile/include/toCompile/source_toCompile.h:23:27: fatal error: "gen/gen.h": No such file or directory

I have tried to apply a previous question A but I don't understand what should be inside foo.h.in. It still can't find the header.
Also tried to add (include ${CATKIN_DEVEL_PREFIX}/include) but it makes no difference.

cmake_minimum_required(VERSION 2.8.3)
project(mav_planning_utils)

find_package(catkin REQUIRED COMPONENTS roscpp gen)

include_directories(include ${Eigen_INCLUDE_DIRS} ${catkin_INCLUDE_DIRS})
include_directories(include ${CATKIN_DEVEL_PREFIX}/include)

catkin_package(
    CATKIN_DEPENDS roscpp gen
    INCLUDE_DIRS  include ${Eigen_INCLUDE_DIRS} 
    LIBRARIES yaml-cpp ${PROJECT_NAME} ${PROJECT_NAME}_timing ${PROJECT_NAME}_rpoly
    CFG_EXTRAS export_flags.cmake 
)
add_subdirectory(src/library)
add_subdirectory(src/test)
add_subdirectory(src/nodes)

The export_flags just has SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")

I assuming the headers are already in the correct place (devel/include) it's just a question of pointing catkin in the right direction. Also, this worked fine in indigo and broke in kinetic.

Thank you for any help!