diff --git a/CMakeLists.txt b/CMakeLists.txt
index 97ea344..24e9361 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -13,6 +13,7 @@ endif(NOT DEFINED N2N_OPTION_AES)
 add_definitions(-DN2N_VERSION="${N2N_VERSION}" -DN2N_OSNAME="${N2N_OSNAME}")
 
 if(N2N_OPTION_AES)
+find_package(OpenSSL REQUIRED)
 add_definitions(-DN2N_HAVE_AES)
 endif(N2N_OPTION_AES)