diff --git a/CMakeLists.txt b/CMakeLists.txt
index f5bd0d9..9ba01f1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,9 @@
 cmake_minimum_required(VERSION 2.7)
+
+if(TARGET lex)
+  return()
+endif(TARGET lex)
+
 project(liblex)
 
 add_library(lex STATIC src/pattern.c src/pairmap.c src/eval.c)