Index: cmake/Modules/GetClangResourceDir.cmake
===================================================================
--- cmake/Modules/GetClangResourceDir.cmake
+++ cmake/Modules/GetClangResourceDir.cmake
@@ -12,7 +12,9 @@
   if(DEFINED CLANG_RESOURCE_DIR AND NOT CLANG_RESOURCE_DIR STREQUAL "")
     set(ret_dir bin/${CLANG_RESOURCE_DIR})
   else()
-    string(REGEX MATCH "^[0-9]+" CLANG_VERSION_MAJOR ${PACKAGE_VERSION})
+    if (NOT CLANG_VERSION_MAJOR)
+      string(REGEX MATCH "^[0-9]+" CLANG_VERSION_MAJOR ${PACKAGE_VERSION})
+    endif()
     set(ret_dir lib${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION_MAJOR})
   endif()