diff --git a/CMakeLists.txt b/CMakeLists.txt
index 908f7a4d0..4699a712b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -41,7 +41,7 @@ if(ENABLE_ZLIB_SUPPORT)
   find_package(ZLIB)
 
   if(ZLIB_FOUND)
-    include_directories(ZLIB_INCLUDE_DIR)
+    include_directories(${ZLIB_INCLUDE_DIR})
   endif(ZLIB_FOUND)
 endif(ENABLE_ZLIB_SUPPORT)