diff --git a/lemon/CMakeLists.txt b/lemon/CMakeLists.txt
--- a/lemon/CMakeLists.txt
+++ b/lemon/CMakeLists.txt
@@ -20,7 +20,7 @@
 
 IF(HAVE_GLPK)
   SET(LEMON_SOURCES ${LEMON_SOURCES} glpk.cc)
-  INCLUDE_DIRECTORIES(${GLPK_INCLUDE_DIR})
+  INCLUDE_DIRECTORIES(${GLPK_INCLUDE_DIRS})
   IF(WIN32)
     INSTALL(FILES ${GLPK_BIN_DIR}/glpk.dll DESTINATION bin)
     INSTALL(FILES ${GLPK_BIN_DIR}/libltdl3.dll DESTINATION bin)