diff --git a/sandboxed_api/sandbox2/BUILD.bazel b/sandboxed_api/sandbox2/BUILD.bazel
index 212841c..959244b 100644
--- a/sandboxed_api/sandbox2/BUILD.bazel
+++ b/sandboxed_api/sandbox2/BUILD.bazel
@@ -774,7 +774,10 @@ cc_test(
     name = "sanitizer_test",
     srcs = ["sanitizer_test.cc"],
     copts = sapi_platform_copts(),
-    data = ["//sandboxed_api/sandbox2/testcases:sanitizer"],
+    data = [
+        "//sandboxed_api/sandbox2/testcases:close_fds",
+        "//sandboxed_api/sandbox2/testcases:sanitizer",
+    ],
     tags = ["no_qemu_user_mode"],
     deps = [
         ":comms",
diff --git a/sandboxed_api/sandbox2/CMakeLists.txt b/sandboxed_api/sandbox2/CMakeLists.txt
index f890350..276d2a6 100644
--- a/sandboxed_api/sandbox2/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/CMakeLists.txt
@@ -874,6 +874,7 @@ if(SAPI_ENABLE_TESTS)
   )
   add_dependencies(sandbox2_sanitizer_test
     sandbox2::testcase_sanitizer
+    sandbox2::testcase_close_fds
   )
   target_link_libraries(sandbox2_sanitizer_test PRIVATE
     absl::memory
diff --git a/sandboxed_api/sandbox2/sanitizer_test.cc b/sandboxed_api/sandbox2/sanitizer_test.cc
index 870b9bd..e83b548 100644
--- a/sandboxed_api/sandbox2/sanitizer_test.cc
+++ b/sandboxed_api/sandbox2/sanitizer_test.cc
@@ -15,7 +15,6 @@
 #include "sandboxed_api/sandbox2/sanitizer.h"
 
 #include <fcntl.h>
-#include <linux/fs.h>
 #include <sys/socket.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -45,8 +44,6 @@
 using ::sapi::GetTestSourcePath;
 using ::testing::Eq;
 using ::testing::Gt;
-using ::testing::IsFalse;
-using ::testing::IsTrue;
 using ::testing::Ne;
 
 namespace sandbox2 {
@@ -59,12 +56,13 @@ int RunTestcase(const std::string& path, const std::vector<std::string>& args) {
     PLOG(ERROR) << "fork()";
     return 1;
   }
+  const char** argv = util::VecStringToCharPtrArr(args);
   if (pid == 0) {
-    const char** argv = util::VecStringToCharPtrArr(args);
     execv(path.c_str(), const_cast<char**>(argv));
     PLOG(ERROR) << "execv('" << path << "')";
     exit(EXIT_FAILURE);
   }
+  delete[] argv;
 
   for (;;) {
     int status;
@@ -135,6 +133,26 @@ TEST(SanitizerTest, TestSandboxedBinary) {
   EXPECT_THAT(result.reason_code(), Eq(0));
 }
 
+// Test that sanitizer::CloseAllFDsExcept() closes all file descriptors except
+// the ones listed.
+TEST(SanitizerTest, TestCloseFDs) {
+  // Open a few file descriptors in non-close-on-exec mode.
+  int sock_fd[2];
+  ASSERT_THAT(socketpair(AF_UNIX, SOCK_STREAM, 0, sock_fd), Ne(-1));
+  ASSERT_THAT(open("/dev/full", O_RDONLY), Ne(-1));
+  int null_fd = open("/dev/null", O_RDWR);
+  ASSERT_THAT(null_fd, Ne(-1));
+
+  const std::string path = GetTestSourcePath("sandbox2/testcases/close_fds");
+  std::vector<std::string> args;
+  std::vector<int> exceptions = {STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO,
+                                 null_fd};
+  for (auto fd : exceptions) {
+    args.push_back(absl::StrCat(fd));
+  }
+  EXPECT_THAT(RunTestcase(path, args), Eq(0));
+}
+
 TEST(SanitizerTest, TestGetProcStatusLine) {
   // Test indirectly, GetNumberOfThreads() looks for the "Threads" value.
   EXPECT_THAT(sanitizer::GetNumberOfThreads(getpid()), Gt(0));
diff --git a/sandboxed_api/sandbox2/testcases/BUILD.bazel b/sandboxed_api/sandbox2/testcases/BUILD.bazel
index 4581442..2f9957e 100644
--- a/sandboxed_api/sandbox2/testcases/BUILD.bazel
+++ b/sandboxed_api/sandbox2/testcases/BUILD.bazel
@@ -164,6 +164,19 @@ cc_binary(
     linkstatic = 1,
 )
 
+cc_binary(
+    name = "close_fds",
+    testonly = 1,
+    srcs = ["close_fds.cc"],
+    copts = sapi_platform_copts(),
+    deps = [
+        "//sandboxed_api/sandbox2:sanitizer",
+        "@com_google_absl//absl/container:flat_hash_set",
+        "@com_google_absl//absl/strings",
+        "@com_google_glog//:glog",
+    ],
+)
+
 # security: disable=cc-static-no-pie
 cc_binary(
     name = "sleep",
diff --git a/sandboxed_api/sandbox2/testcases/CMakeLists.txt b/sandboxed_api/sandbox2/testcases/CMakeLists.txt
index f954faa..0ec9d75 100644
--- a/sandboxed_api/sandbox2/testcases/CMakeLists.txt
+++ b/sandboxed_api/sandbox2/testcases/CMakeLists.txt
@@ -185,6 +185,24 @@ target_link_libraries(sandbox2_testcase_sanitizer PRIVATE
   ${_sandbox2_linkopts}
 )
 
+# sandboxed_api/sandbox2/testcases:close_fds
+add_executable(sandbox2_testcase_close_fds
+  close_fds.cc
+)
+add_executable(sandbox2::testcase_close_fds ALIAS sandbox2_testcase_close_fds)
+set_target_properties(sandbox2_testcase_close_fds PROPERTIES
+  OUTPUT_NAME close_fds
+)
+target_link_libraries(sandbox2_testcase_close_fds PRIVATE
+  sapi::base
+  ${_sandbox2_linkopts}
+  absl::strings
+  absl::flat_hash_set
+  glog::glog
+  sandbox2::sanitizer
+)
+
+
 # sandboxed_api/sandbox2/testcases:sleep
 add_executable(sandbox2_testcase_sleep
   sleep.cc
diff --git a/sandboxed_api/sandbox2/testcases/close_fds.cc b/sandboxed_api/sandbox2/testcases/close_fds.cc
new file mode 100644
index 0000000..b106564
--- /dev/null
+++ b/sandboxed_api/sandbox2/testcases/close_fds.cc
@@ -0,0 +1,32 @@
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <unistd.h>
+
+#include <cerrno>
+
+#include <glog/logging.h>
+#include "absl/container/flat_hash_set.h"
+#include "absl/strings/numbers.h"
+#include "sandboxed_api/sandbox2/sanitizer.h"
+
+bool IsFdOpen(int fd) {
+  int ret = fcntl(fd, F_GETFD);
+  if (ret == -1) {
+    CHECK(errno == EBADF);
+    return false;
+  }
+  return true;
+}
+
+int main(int argc, char* argv[]) {
+  absl::flat_hash_set<int> exceptions;
+  for (int i = 0; i < argc; ++i) {
+    int fd;
+    CHECK(absl::SimpleAtoi(argv[i], &fd));
+    exceptions.insert(fd);
+  }
+  CHECK(sandbox2::sanitizer::CloseAllFDsExcept(exceptions).ok());
+  for (int i = 0; i < INR_OPEN_MAX; i++) {
+    CHECK_EQ(IsFdOpen(i), exceptions.find(i) != exceptions.end());
+  }
+}