diff --git a/Code/Mantid/docs/CMakeLists.txt b/Code/Mantid/docs/CMakeLists.txt
index da7f8a2ef867..bb6a1cf0e30d 100644
--- a/Code/Mantid/docs/CMakeLists.txt
+++ b/Code/Mantid/docs/CMakeLists.txt
@@ -108,7 +108,7 @@ if ( SPHINX_FOUND )
   # Add individual test targets for each file, if requested.
   # They will require the Framework target to be built
   ###############################################################################
-  set ( SEPARATE_DOC_TESTS TRUE BOOL
+  set ( SEPARATE_DOC_TESTS TRUE CACHE BOOL
        "If true, a separate test for each documentation file is added to ctest.")
 
   if( SEPARATE_DOC_TESTS )