diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8ad8f86f72..640e8fde8e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -47,7 +47,7 @@ endif (${CMAKE_CXX_COMPILER_ID} MATCHES "Clang")
 # ================================================================================
 
 # Allow developers to use Boost < 1.48
-if (NOT ${BOOST_MIN_VERSION})
+if (NOT BOOST_MIN_VERSION)
     set(BOOST_MIN_VERSION 1.48)
 endif()