diff --git a/CMakeLists.txt b/CMakeLists.txt
index 933a8f3845..7bd6c3d794 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -143,9 +143,10 @@ LYX_OPTION(ENABLE_KEYTESTS  "Enable for keytests" OFF ALL)
 LYX_OPTION(ASAN             "Use address sanitizer" OFF ALL)
 LYX_COMBO(USE_QT            "Use Qt version as frontend" QT4 QT5)
 #LYX_OPTION(3RDPARTY_BUILD   "Build 3rdparty libs" OFF ALL)
-LYX_OPTION(EXTERNAL_Z       "Build 3rdparty lib zlib" ON ALL)
-LYX_OPTION(EXTERNAL_ICONV   "Build 3rdparty lib iconvlib" ON ALL)
-LYX_OPTION(EXTERNAL_HUNSPELL "Build 3rdparty lib hunspelllib" ON ALL)
+LYX_OPTION(EXTERNAL_Z       "Do not build 3rdparty lib zlib" ON ALL)
+LYX_OPTION(EXTERNAL_ICONV   "Do not build 3rdparty lib iconvlib" ON ALL)
+LYX_OPTION(EXTERNAL_HUNSPELL "Do not build 3rdparty lib hunspelllib" ON ALL)
+LYX_OPTION(EXTERNAL_MYTHES  "Do not build 3rdparty lib mytheslib" OFF ALL)
 
 # GCC specific
 LYX_OPTION(PROFILE              "Build profile version" OFF GCC)
@@ -183,6 +184,12 @@ if(LYX_DMG)
 	set(LYX_CPACK ON)
 endif()
 
+if (LYX_EXTERNAL_MYTHES)
+  message(FATAL_ERROR "Compilation with system mythes not supported yet")
+else()
+  set(MYTHES_DIR "${TOP_SRC_DIR}/3rdparty/mythes/1.2.5")
+endif()
+
 if(LYX_CPACK)
 	set(LYX_INSTALL ON)
 endif()
@@ -284,7 +291,7 @@ if(UNIX OR MINGW)
 		  # see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53631
 		  set(LYX_USE_STD_REGEX 0)
 	  else()
-		  set(LYX_USE_STD_REGEX 1)
+		  set(LYX_USE_STD_REGEX 0)
 	  endif()
 	endif()
 	set(LYX_GCC11_MODE "${CXX11_FLAG}")
diff --git a/development/cmake/config.h.cmake b/development/cmake/config.h.cmake
index dbd2c83bc7..f0a504a81a 100644
--- a/development/cmake/config.h.cmake
+++ b/development/cmake/config.h.cmake
@@ -96,7 +96,7 @@ ${Include_used_spellchecker}
 
 #endif // config.h guard
 
-
+#define MYTHES_H_LOCATION <${MYTHES_DIR}/mythes.hxx>
 
 // Unguarded cleanup of global namespace:
 
diff --git a/src/support/CMakeLists.txt b/src/support/CMakeLists.txt
index d93fbe42b1..1cb6c4aef3 100644
--- a/src/support/CMakeLists.txt
+++ b/src/support/CMakeLists.txt
@@ -18,8 +18,8 @@ endif()
 
 file(GLOB support_headers ${TOP_SRC_DIR}/src/support/${LYX_HPP_FILES})
 
-file(GLOB support_mythes_sources ${TOP_SRC_DIR}/src/support/mythes/*.cxx)
-file(GLOB support_mythes_headers ${TOP_SRC_DIR}/src/support/mythes/*.hxx)
+file(GLOB support_mythes_sources ${MYTHES_DIR}/*.cxx)
+file(GLOB support_mythes_headers ${MYTHES_DIR}/*.hxx)
 
 file(GLOB support_linkback_sources ${TOP_SRC_DIR}/src/support/linkback/*.m*)
 file(GLOB support_linkback_headers ${TOP_SRC_DIR}/src/support/linkback/*.h)
@@ -58,7 +58,7 @@ lyx_automoc(${support_sources})
 include_directories(
 	${TOP_SRC_DIR}/src/support
 	${TOP_BINARY_DIR}/src/support
-	${TOP_SRC_DIR}/src/support/mythes
+	${MYTHES_DIR}
 	${QT_INCLUDES}
 	${ICONV_INCLUDE_DIR}
 	${ZLIB_INCLUDE_DIR})