diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 6b96a5147753e..4873bec39f8af 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -713,6 +713,9 @@ macro(add_custom_libcxx name prefix)
     USES_TERMINAL_INSTALL 1
     LIST_SEPARATOR |
     EXCLUDE_FROM_ALL TRUE
+    # Ensure that DESTDIR=... set in the out environment does not affect this
+    # target (we always need to install to the build directory).
+    INSTALL_COMMAND env DESTDIR= ${CMAKE_COMMAND} --build ${prefix}/build --target install
     INSTALL_BYPRODUCTS "${prefix}/lib/libc++.a" "${prefix}/lib/libc++abi.a"
     )