diff --git a/subdoc/CMakeLists.txt b/subdoc/CMakeLists.txt
index 130ec3b0f..17b4d4464 100644
--- a/subdoc/CMakeLists.txt
+++ b/subdoc/CMakeLists.txt
@@ -45,6 +45,8 @@ target_sources(subdoc_lib PUBLIC
     "lib/gen/markdown_to_html.cc"
     "lib/gen/markdown_to_html.h"
     "lib/gen/options.h"
+    "lib/clang_resource_dir.cc"
+    "lib/clang_resource_dir.h"
     "lib/database.h"
     "lib/friendly_names.h"
     "lib/linked_type.cc"
diff --git a/subdoc/lib/clang_resource_dir.cc b/subdoc/lib/clang_resource_dir.cc
new file mode 100644
index 000000000..a33a47a26
--- /dev/null
+++ b/subdoc/lib/clang_resource_dir.cc
@@ -0,0 +1,82 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "subdoc/lib/clang_resource_dir.h"
+
+#include <filesystem>
+#include <fstream>
+
+#include "subdoc/llvm.h"
+
+namespace subdoc {
+
+Option<std::string> ClangResourceDir::find_resource_dir(std::string_view tool) {
+  if (auto it = cache_.find(tool); it != cache_.end()) {
+    return sus::some(it->second);
+  }
+
+  std::filesystem::path tool_path(tool);
+  std::string stem = tool_path.stem().string();
+  if (!stem.starts_with("clang")) return sus::none();
+
+  if (!std::filesystem::exists(tool_path)) {
+    fmt::println(stderr, "WARNING: can't find clang compiler at '{}'", tool);
+    return sus::none();
+  }
+
+  std::array<llvm::StringRef, 2> args = {tool, "-print-resource-dir"};
+  if (stem.starts_with("clang-cl")) {
+    args[1] = "/clang:-print-resource-dir";
+  }
+
+  llvm::SmallString<100> out;
+  {
+    std::error_code code =
+        llvm::sys::fs::createTemporaryFile("stdout", "txt", out);
+    if (code) {
+      fmt::println(stderr, "WARNING: unable to make temp file: {}",
+                   code.message());
+      return sus::none();
+    }
+  }
+  std::array<std::optional<llvm::StringRef>, 3> redirects = {std::nullopt, out,
+                                                             std::nullopt};
+  {
+    i32 code =
+        llvm::sys::ExecuteAndWait(tool, args, /*env=*/std::nullopt, redirects);
+    if (code != 0) {
+      fmt::println(
+          stderr, "WARNING: failed to run clang compiler at '{}', exit code {}",
+          tool, code);
+      return sus::none();
+    }
+  }
+
+  auto out_file = std::ifstream(out.c_str());
+  std::string resource_dir;
+  if (!std::getline(out_file, resource_dir)) {
+    fmt::println(stderr,
+                 "WARNING: 'clang -print-resource-dir' did not return anything "
+                 "for clang compiler at '{}'",
+                 tool);
+    return sus::none();
+  }
+
+  auto trimmed_resource_dir = llvm::StringRef(resource_dir).trim();
+
+  cache_.emplace(tool, std::string(trimmed_resource_dir));
+  return sus::some(std::string(trimmed_resource_dir));
+}
+
+}  // namespace subdoc
diff --git a/subdoc/lib/clang_resource_dir.h b/subdoc/lib/clang_resource_dir.h
new file mode 100644
index 000000000..43641c47c
--- /dev/null
+++ b/subdoc/lib/clang_resource_dir.h
@@ -0,0 +1,43 @@
+// Copyright 2023 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <map>
+#include <string>
+#include <string_view>
+
+#include "sus/prelude.h"
+
+namespace subdoc {
+
+/// Find, store, and return the "resource dir" for finding system headers from
+/// Clang.
+///
+/// Clang tools need to know where the "resource dir" is in order to find
+/// system headers there, if Clang was the compiler that's being used for
+/// building the target.
+///
+/// For other compilers, the headers come from the system header location, but
+/// Clang has a resource dir that is known to the compiler, and which Subdoc
+/// can't know apriori. So it has to query the Clang compiler to get it.
+class ClangResourceDir {
+ public:
+  Option<std::string> find_resource_dir(std::string_view tool);
+
+  std::map<std::string /* tool */, std::string /* resource_dir */, std::less<>>
+      cache_;
+};
+
+}  // namespace subdoc
diff --git a/subdoc/lib/run.cc b/subdoc/lib/run.cc
index 78c5ff509..e076da4d2 100644
--- a/subdoc/lib/run.cc
+++ b/subdoc/lib/run.cc
@@ -14,9 +14,11 @@
 
 #include "subdoc/lib/run.h"
 
+#include <filesystem>
 #include <memory>
 #include <utility>
 
+#include "subdoc/lib/clang_resource_dir.h"
 #include "subdoc/lib/visit.h"
 #include "sus/collections/compat_vector.h"
 #include "sus/iter/iterator.h"
@@ -43,8 +45,7 @@ sus::Result<Database, DiagnosticResults> run_test(
   auto vfs = llvm::IntrusiveRefCntPtr(new llvm::vfs::InMemoryFileSystem());
   vfs->addFile(pretend_file_name, 0, llvm::MemoryBuffer::getMemBuffer(content));
 
-  return run_files(*comp_db,
-                   Vec<std::string>(sus::move(pretend_file_name)),
+  return run_files(*comp_db, Vec<std::string>(sus::move(pretend_file_name)),
                    std::move(vfs), options);
 }
 
@@ -64,8 +65,7 @@ struct DiagnosticTracker : public clang::TextDiagnosticPrinter {
 };
 
 sus::Result<Database, DiagnosticResults> run_files(
-    const clang::tooling::CompilationDatabase& comp_db,
-    Vec<std::string> paths,
+    const clang::tooling::CompilationDatabase& comp_db, Vec<std::string> paths,
     llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
     const RunOptions& options) noexcept {
   // Clang DiagnoticsConsumer that prints out the full error and context, which
@@ -80,13 +80,15 @@ sus::Result<Database, DiagnosticResults> run_files(
       std::make_shared<clang::PCHContainerOperations>(), std::move(fs));
   tool.setDiagnosticConsumer(&*diags);
 
-  auto adj = [](clang::tooling::CommandLineArguments args, llvm::StringRef) {
+  ClangResourceDir resource_dir;
+
+  auto adj = [&resource_dir](clang::tooling::CommandLineArguments args,
+                             llvm::StringRef) {
     // Clang-cl doesn't understand this argument, but it may appear in the
     // command-line for MSVC in C++20 codebases (like subspace).
     std::erase(args, "/Zc:preprocessor");
 
-    const std::string& tool = args[0];
-    if (tool.find("cl.exe") != std::string::npos) {
+    if (std::filesystem::path(args[0]).filename().string() == "cl.exe") {
       // TODO: https://github.com/llvm/llvm-project/issues/59689 clang-cl
       // requires this define in order to use offsetof() from constant
       // expressions, which subspace uses for the never-value optimization.
@@ -130,6 +132,12 @@ sus::Result<Database, DiagnosticResults> run_files(
       return a.starts_with("@") && a.ends_with(".modmap");
     });
 
+    if (Option<std::string> dir = resource_dir.find_resource_dir(args[0]);
+        dir.is_some()) {
+      args.push_back("-resource-dir");
+      args.push_back(dir.as_value());
+    }
+
     return std::move(args);
   };
   tool.appendArgumentsAdjuster(adj);
diff --git a/subdoc/llvm.h b/subdoc/llvm.h
index b9d13c5c9..11bc41c06 100644
--- a/subdoc/llvm.h
+++ b/subdoc/llvm.h
@@ -58,6 +58,7 @@
 #include "llvm/Support/Error.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Program.h"
 #include "llvm/Support/SHA1.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/VirtualFileSystem.h"