diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -124,6 +124,7 @@
 
 ADD_SUBDIRECTORY(lemon)
 IF(${CMAKE_SOURCE_DIR} STREQUAL ${PROJECT_SOURCE_DIR})
+  ADD_SUBDIRECTORY(contrib)
   ADD_SUBDIRECTORY(demo)
   ADD_SUBDIRECTORY(tools)
   ADD_SUBDIRECTORY(doc)