diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9597520..45172d5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,7 +49,7 @@ if(N2N_OPTION_USE_PTHREAD)
   find_library(PTHREAD_LIB pthread)
   if(NOT PTHREAD_LIB)
     MESSAGE(FATAL_ERROR "libpthread not found.")
-  endif(PTHREAD_LIB)
+  endif(NOT PTHREAD_LIB)
   MESSAGE(INFO "Using libpthread.")
   ADD_DEFINITIONS("-DHAVE_PTHREAD")
   target_link_libraries(n2n pthread)