diff --git a/toolchain/BUILD.bazel b/toolchain/BUILD.bazel
index fa00156236..c9e4348172 100644
--- a/toolchain/BUILD.bazel
+++ b/toolchain/BUILD.bazel
@@ -1,5 +1,6 @@
 load("@bazel_lib//:bzl_library.bzl", "bzl_library")
+load("@bazel_skylib//lib:selects.bzl", "selects")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag", "string_setting")
 load("@rules_cc//cc/toolchains:actions.bzl", "cc_action_type_set")
 load("@rules_cc//cc/toolchains:artifacts.bzl", "cc_artifact_name_pattern")
 load("@rules_cc//cc/toolchains/impl:documented_api.bzl", "cc_args_list")
@@ -64,6 +65,15 @@ config_setting(
     visibility = ["//visibility:public"],
 )
-
+
+selects.config_setting_group(
+    name = "runtimes_all_with_rusty_v8_custom_libcxx",
+    match_all = [
+        ":runtimes_all",
+        "@@//third_party/v8:use_rusty_v8_custom_libcxx",
+    ],
+    visibility = ["//visibility:public"],
+)
+
 config_setting(
     name = "runtimes_stage1",
     flag_values = {
@@ -270,11 +280,16 @@ cc_args_list(
 
 # TODO(cerisier): extract those into proper semantic args list.
 # TODO(zbarsky): This must match llvm/toolchains/llvm.bzl
+_DEFAULT_CXXSTDLIB_HEADER_ARGS = select({
+    "@@//third_party/v8:use_rusty_v8_custom_libcxx": [],
+    "//conditions:default": [
+        "//toolchain/args:cxxstdlib_headers_include_search_paths",
+    ],
+})
+
 cc_args_list(
     name = "linux_toolchain_args",
-    args = [
-        "//toolchain/args:cxxstdlib_headers_include_search_paths",
-    ] + select({
+    args = _DEFAULT_CXXSTDLIB_HEADER_ARGS + select({
         "//platforms/config:musl": [
             "//toolchain/args/linux:kernel_headers_include_search_paths",
             "//toolchain/args/linux:musl_libc_headers_include_search_paths",
@@ -302,8 +317,7 @@ cc_args_list(
 # TODO(zbarsky): This must match llvm/toolchains/llvm.bzl
 cc_args_list(
     name = "windows_toolchain_args",
-    args = [
-        "//toolchain/args:cxxstdlib_headers_include_search_paths",
+    args = _DEFAULT_CXXSTDLIB_HEADER_ARGS + [
         "//toolchain/args/windows:mingw_headers_include_search_paths",
     ],
 )
diff --git a/toolchain/llvm/llvm.bzl b/toolchain/llvm/llvm.bzl
index d36d8b94bd..900aa908d5 100644
--- a/toolchain/llvm/llvm.bzl
+++ b/toolchain/llvm/llvm.bzl
@@ -297,18 +297,23 @@ def declare_llvm_targets(*, suffix = ""):
         ],
     )
 
+    default_cxxstdlib_target_headers = select({
+        "@llvm//toolchain:runtimes_all_with_rusty_v8_custom_libcxx": [],
+        "@llvm//toolchain:runtimes_stage1": [],
+        "@llvm//toolchain:runtimes_stage1_hosted": [],
+        "@llvm//toolchain:runtimes_none": [],
+        "//conditions:default": [
+            "@llvm//runtimes/cxxstdlib:headers_include_search_directory",
+            "@llvm//runtimes/cxxstdlib:abi_headers_include_search_directory",
+        ],
+    })
+
     # This must match //toolchain:linux_toolchain_args
     include_path(
         name = "linux_target_headers",
         srcs = [
             ":builtin_resource_dir",
-        ] + select({
-            "@llvm//toolchain:runtimes_all": [
-                "@llvm//runtimes/cxxstdlib:headers_include_search_directory",
-                "@llvm//runtimes/cxxstdlib:abi_headers_include_search_directory",
-            ],
-            "//conditions:default": [],
-        }) + [
+        ] + default_cxxstdlib_target_headers + [
             "@kernel_headers//:kernel_headers_directory",
             "@llvm//sanitizers:sanitizers_headers_include_search_directory",
         ] + select({
@@ -324,13 +329,7 @@ def declare_llvm_targets(*, suffix = ""):
         name = "windows_target_headers",
         srcs = [
             ":builtin_resource_dir",
-        ] + select({
-            "@llvm//toolchain:runtimes_all": [
-                "@llvm//runtimes/cxxstdlib:headers_include_search_directory",
-                "@llvm//runtimes/cxxstdlib:abi_headers_include_search_directory",
-            ],
-            "//conditions:default": [],
-        }) + [
+        ] + default_cxxstdlib_target_headers + [
             "@mingw//:mingw_generated_headers_crt_directory",
             "@mingw//:mingw_w64_headers_include_directory",
             "@mingw//:mingw_w64_headers_crt_directory",