diff --git a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake b/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
--- a/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
+++ b/libcxx/cmake/Modules/HandleOutOfTreeLLVM.cmake
@@ -14,6 +14,8 @@
 set(LLVM_PATH ${LLVM_PATH} CACHE PATH "Path to LLVM source tree")
 set(LLVM_MAIN_SRC_DIR ${LLVM_PATH})
 set(LLVM_CMAKE_PATH "${LLVM_PATH}/cmake/modules")
+set(LLVM_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
+set(LLVM_LIBRARY_OUTPUT_INTDIR "${CMAKE_CURRENT_BINARY_DIR}/lib")
 
 if (EXISTS "${LLVM_CMAKE_PATH}")
   list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -58,6 +58,12 @@
   endif()
 endif()
 
+if (CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  set(LLVM_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
+  set(LLVM_TOOLS_BINARY_DIR ${LLVM_BINARY_DIR}/bin)
+  set(LLVM_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/lib)
+endif()
+
 # Setting these variables will allow the sub-build to put their outputs into
 # the library and bin directories of the top-level build.
 set(LLVM_LIBRARY_OUTPUT_INTDIR ${LLVM_LIBRARY_DIR})