diff --git a/CMakeLists.txt b/CMakeLists.txt
index e0e565657f..7e2d3d1302 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -275,7 +275,7 @@ find_package(CXX11Compiler)
 if(NOT CXX11COMPILER_FOUND)
 	message(FATAL_ERROR "A C++11 compatible compiler is required.")
 endif()
-set(LYX_GCC11_MODE)
+unset(LYX_GCC11_MODE)
 if(UNIX OR MINGW)
 	if (CMAKE_CXX_COMPILER_ID MATCHES "^([cC]lang|AppleClang)$")
 	  # ignore the GCC_VERSION for clang
@@ -393,6 +393,7 @@ foreach(_c_l ${_config_lines} )
 		set(LYX_DATE "${CMAKE_MATCH_1}")
 	endif()
 endforeach(_c_l)
+unset(_config_lines)
 
 FIND_PROGRAM(LYX_GITVERSION git)
 #message(STATUS "gitversion = ${LYX_GITVERSION}")
@@ -1068,7 +1069,7 @@ endif()
 include(${LYX_CMAKE_DIR}/ConfigureChecks.cmake)
 configure_file(${LYX_CMAKE_DIR}/configCompiler.h.cmake ${TOP_BINARY_DIR}/configCompiler.h)
 
-set(opts)
+unset(opts)
 foreach(_option ${LYX_OPTIONS})
   if(${_option}_show_message)
     string(SUBSTRING "${_option}                            " 0 31 _var)
@@ -1103,6 +1104,8 @@ list(APPEND tmp_vi "  LyX files dir:           ${CMAKE_INSTALL_PREFIX}/${dest_da
 string(REPLACE ";" "\\n" VERSION_INFO "${tmp_vi}")
 
 configure_file(${LYX_CMAKE_DIR}/config.h.cmake ${TOP_BINARY_DIR}/config.h)
+unset(opts)
+unset(tmp_vi)
 
 if(QTVERSION MATCHES "^([0-9]+)\\.([0-9]+)\\.([0-9]+).*")
 	MATH(EXPR QT4_VERSION "(${CMAKE_MATCH_1}<<16)|(${CMAKE_MATCH_2}<<8)|${CMAKE_MATCH_3}")