-LYX_OPTION(EXTERNAL_Z "OFF := Build 3rdparty lib zlib" ON ALL)
-LYX_OPTION(EXTERNAL_DTL "OFF := Build 3rdparty commands dt2dv and dv2dt" ON ALL)
-LYX_OPTION(EXTERNAL_ICONV "OFF := Build 3rdparty lib iconvlib" ON ALL)
-LYX_OPTION(EXTERNAL_HUNSPELL "OFF := Build 3rdparty lib hunspelllib" ON ALL)
+LYX_OPTION(EXTERNAL_Z "OFF := Build 3rdparty lib zlib" ${DefaultExternalLibs} ALL)
+LYX_OPTION(EXTERNAL_DTL "OFF := Build 3rdparty commands dt2dv and dv2dt" ${DefaultExternalLibs} ALL)
+LYX_OPTION(EXTERNAL_ICONV "OFF := Build 3rdparty lib iconvlib" ${DefaultExternalLibs} ALL)
+LYX_OPTION(EXTERNAL_HUNSPELL "OFF := Build 3rdparty lib hunspelllib" ${DefaultExternalLibs} ALL)