diff --git a/lldb/test/CMakeLists.txt b/lldb/test/CMakeLists.txt
--- a/lldb/test/CMakeLists.txt
+++ b/lldb/test/CMakeLists.txt
@@ -139,6 +139,9 @@
   )
 endif()
 
+set(LLDB_TEST_LIBCXX_ROOT_DIR "${LLVM_BINARY_DIR}" CACHE PATH
+    "The build root for libcxx. Used in standalone builds to point the API tests to a custom build of libcxx.")
+
 # Add dependencies if we test with the in-tree clang.
 # This works with standalone builds as they import the clang target.
 if(TARGET clang)
@@ -169,9 +172,18 @@
     # FIXME: Standalone builds should import the cxx target as well.
     if(LLDB_BUILT_STANDALONE)
       # For now check that the include directory exists.
-      set(cxx_dir "${LLVM_BINARY_DIR}/include/c++")
-      if(NOT EXISTS ${cxx_dir})
-        message(WARNING "LLDB test suite requires libc++ in llvm/projects/libcxx or an existing build symlinked to ${cxx_dir}")
+      set(cxx_dir "${LLDB_TEST_LIBCXX_ROOT_DIR}/include/c++")
+      if(EXISTS ${cxx_dir})
+        # These variables make sure the API tests can run against a custom
+        # build of libcxx even for standalone builds.
+        set(LLDB_HAS_LIBCXX ON)
+        set(LIBCXX_LIBRARY_DIR "${LLDB_TEST_LIBCXX_ROOT_DIR}/lib${LIBCXX_LIBDIR_SUFFIX}")
+        set(LIBCXX_GENERATED_INCLUDE_DIR "${LLDB_TEST_LIBCXX_ROOT_DIR}/include/c++/v1")
+      else()
+        message(FATAL_ERROR
+            "Couldn't find libcxx build in '${LLDB_TEST_LIBCXX_ROOT_DIR}'. To run the "
+            "test-suite for a standalone LLDB build please build libcxx and point "
+            "LLDB_TEST_LIBCXX_ROOT_DIR to it.")
       endif()
     else()
       # We require libcxx for the test suite, so if we aren't building it,