diff --git a/kalzium/ConfigureChecks.cmake b/kalzium/ConfigureChecks.cmake
index a51abf1b..bb1da003 100644
--- a/kalzium/ConfigureChecks.cmake
+++ b/kalzium/ConfigureChecks.cmake
@@ -64,7 +64,7 @@ if( WITH_OCAML_SOLVER )
       )
     endif( )
 
-    if( NOT DEFINED FACILE_LIBRARIES OR NOT DEFINED FACILE_INCLUDE_DIR )
+    if( (NOT FACILE_LIBRARIES) OR (NOT FACILE_INCLUDE_DIR) )
       tde_message_fatal( "Facile is requested, but was not found on your system" )
     endif( )