diff --git a/cmake/BuildGtest.cmake b/cmake/BuildGtest.cmake
index c14d16dd4be498e7f7920862908baa631b138c5d..5567e76c881bdd5359cffeb2c9fa07a40ec40231 100644
--- a/cmake/BuildGtest.cmake
+++ b/cmake/BuildGtest.cmake
@@ -10,7 +10,7 @@
 
 # compatibility with the GTest package
 set( GTEST_BOTH_LIBRARIES gtest gtest_main )
-set( CXX_TESTS_FLAGS "${CXX_TESTS_FLAGS} -DHAVE_GTEST" )
+set( CXX_TESTS_FLAGS ${CXX_TESTS_FLAGS} -DHAVE_GTEST )
 
 
 # Download and unpack googletest at configure time