Trailing slash seems necessary in the install command to get contents

CMakeLists.txt

@@ -64,4 +64,4 @@ install(TARGETS json-c
     ARCHIVE DESTINATION lib)
 
 install(DIRECTORY . DESTINATION ${CMAKE_INSTALL_PREFIX}/include FILES_MATCHING PATTERN "*.h")
-install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include DESTINATION ${CMAKE_INSTALL_PREFIX}/include FILES_MATCHING PATTERN "*.h")
+install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/include/ DESTINATION ${CMAKE_INSTALL_PREFIX}/include FILES_MATCHING PATTERN "*.h")