diff --git a/sandboxed_api/sandbox2/buffer_test.cc b/sandboxed_api/sandbox2/buffer_test.cc
index 32c5c02..425032d 100644
--- a/sandboxed_api/sandbox2/buffer_test.cc
+++ b/sandboxed_api/sandbox2/buffer_test.cc
@@ -63,6 +63,7 @@ TEST(BufferTest, TestImplementation) {
 
 std::unique_ptr<Policy> BufferTestcasePolicy() {
   auto s2p = PolicyBuilder()
+                 .DisableNamespaces()
                  .AllowStaticStartup()
                  .AllowExit()
                  .AllowSafeFcntl()
diff --git a/sandboxed_api/sandbox2/examples/crc4/crc4sandbox.cc b/sandboxed_api/sandbox2/examples/crc4/crc4sandbox.cc
index 7c2176f..ec87d4b 100644
--- a/sandboxed_api/sandbox2/examples/crc4/crc4sandbox.cc
+++ b/sandboxed_api/sandbox2/examples/crc4/crc4sandbox.cc
@@ -49,6 +49,7 @@ namespace {
 
 std::unique_ptr<sandbox2::Policy> GetPolicy() {
   return sandbox2::PolicyBuilder()
+      .DisableNamespaces()
       .AllowExit()
       .AddPolicyOnSyscalls(
           {__NR_read, __NR_write, __NR_close},
diff --git a/sandboxed_api/sandbox2/ipc_test.cc b/sandboxed_api/sandbox2/ipc_test.cc
index 97ce506..339dbdc 100644
--- a/sandboxed_api/sandbox2/ipc_test.cc
+++ b/sandboxed_api/sandbox2/ipc_test.cc
@@ -44,6 +44,7 @@ TEST(IPCTest, MapFDByNamePreExecve) {
   Comms comms(executor->ipc()->ReceiveFd(kPreferredIpcFd, "ipc_test"));
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -74,6 +75,7 @@ TEST(IPCTest, MapFDByNamePostExecve) {
   Comms comms(executor->ipc()->ReceiveFd(kPreferredIpcFd, "ipc_test"));
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -100,6 +102,7 @@ TEST(IPCTest, NoMappedFDsPreExecve) {
   auto executor = absl::make_unique<Executor>(path, args);
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
diff --git a/sandboxed_api/sandbox2/limits_test.cc b/sandboxed_api/sandbox2/limits_test.cc
index 9b27b9c..ce04358 100644
--- a/sandboxed_api/sandbox2/limits_test.cc
+++ b/sandboxed_api/sandbox2/limits_test.cc
@@ -42,6 +42,7 @@ TEST(LimitsTest, RLimitASMmapUnderLimit) {
   executor->limits()->set_rlimit_as(100ULL << 20);  // 100 MiB
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, sandbox2::PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -59,6 +60,7 @@ TEST(LimitsTest, RLimitASMmapAboveLimit) {
   executor->limits()->set_rlimit_as(100ULL << 20);  // 100 MiB
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, sandbox2::PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -76,6 +78,7 @@ TEST(LimitsTest, RLimitASAllocaSmallUnderLimit) {
   executor->limits()->set_rlimit_as(100ULL << 20);  // 100 MiB
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, sandbox2::PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -93,6 +96,7 @@ TEST(LimitsTest, RLimitASAllocaBigUnderLimit) {
   executor->limits()->set_rlimit_as(100ULL << 20);  // 100 MiB
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, sandbox2::PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -110,6 +114,7 @@ TEST(LimitsTest, RLimitASAllocaBigAboveLimit) {
   executor->limits()->set_rlimit_as(100ULL << 20);  // 100 MiB
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, sandbox2::PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
diff --git a/sandboxed_api/sandbox2/namespace_test.cc b/sandboxed_api/sandbox2/namespace_test.cc
index 702570a..06c28cf 100644
--- a/sandboxed_api/sandbox2/namespace_test.cc
+++ b/sandboxed_api/sandbox2/namespace_test.cc
@@ -83,6 +83,7 @@ TEST(NamespaceTest, UserNamespaceWorks) {
   {
     auto executor = absl::make_unique<Executor>(path, args);
     SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                          .DisableNamespaces()
                                           // Don't restrict the syscalls at all
                                           .DangerDefaultAllowAll()
                                           .TryBuild());
@@ -103,6 +104,7 @@ TEST(NamespaceTest, UserNamespaceIDMapWritten) {
     std::vector<std::string> args = {path, "3", "1000", "1000"};
     auto executor = absl::make_unique<Executor>(path, args);
     SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                          .EnableNamespaces()
                                           // Don't restrict the syscalls at all
                                           .DangerDefaultAllowAll()
                                           .EnableNamespaces()
@@ -122,6 +124,7 @@ TEST(NamespaceTest, UserNamespaceIDMapWritten) {
     std::vector<std::string> args = {path, "3", uid, gid};
     auto executor = absl::make_unique<Executor>(path, args);
     SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                          .DisableNamespaces()
                                           // Don't restrict the syscalls at all
                                           .DangerDefaultAllowAll()
                                           .TryBuild());
@@ -151,6 +154,7 @@ class HostnameTest : public testing::Test {
 
 TEST_F(HostnameTest, None) {
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
diff --git a/sandboxed_api/sandbox2/notify_test.cc b/sandboxed_api/sandbox2/notify_test.cc
index fb285fb..557f7f1 100644
--- a/sandboxed_api/sandbox2/notify_test.cc
+++ b/sandboxed_api/sandbox2/notify_test.cc
@@ -42,6 +42,7 @@ namespace {
 // chosen because unlikely to be called by a regular program.
 std::unique_ptr<Policy> NotifyTestcasePolicy() {
   return PolicyBuilder()
+      .DisableNamespaces()
       .AllowStaticStartup()
       .AllowExit()
       .AllowRead()
diff --git a/sandboxed_api/sandbox2/policy_test.cc b/sandboxed_api/sandbox2/policy_test.cc
index b27be97..6f6758a 100644
--- a/sandboxed_api/sandbox2/policy_test.cc
+++ b/sandboxed_api/sandbox2/policy_test.cc
@@ -41,6 +41,7 @@ namespace {
 
 std::unique_ptr<Policy> PolicyTestcasePolicy() {
   return PolicyBuilder()
+      .DisableNamespaces()
       .AllowStaticStartup()
       .AllowExit()
       .AllowRead()
diff --git a/sandboxed_api/sandbox2/policybuilder_test.cc b/sandboxed_api/sandbox2/policybuilder_test.cc
index 1318b7c..68af600 100644
--- a/sandboxed_api/sandbox2/policybuilder_test.cc
+++ b/sandboxed_api/sandbox2/policybuilder_test.cc
@@ -194,6 +194,7 @@ std::string PolicyBuilderTest::Run(std::vector<std::string> args,
 
 TEST_F(PolicyBuilderTest, TestCanOnlyBuildOnce) {
   PolicyBuilder b;
+  b.EnableNamespaces();
   ASSERT_THAT(b.BuildOrDie(), NotNull());
   ASSERT_DEATH(b.BuildOrDie(), "Can only build policy once");
 }
diff --git a/sandboxed_api/sandbox2/sandbox2_test.cc b/sandboxed_api/sandbox2/sandbox2_test.cc
index 6d29e8f..1a3f290 100644
--- a/sandboxed_api/sandbox2/sandbox2_test.cc
+++ b/sandboxed_api/sandbox2/sandbox2_test.cc
@@ -54,6 +54,7 @@ TEST(SandboxCoreDumpTest, AbortWithoutCoreDumpReturnsSignaled) {
   auto executor = absl::make_unique<Executor>(path, args);
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -75,6 +76,7 @@ TEST(TsyncTest, TsyncNoMemoryChecks) {
   executor->set_enable_sandbox_before_exec(false);
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -101,6 +103,7 @@ TEST(ExecutorTest, ExecutorFdConstructor) {
   auto executor = absl::make_unique<Executor>(fd, args, envs);
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());
@@ -205,8 +208,9 @@ TEST(StarvationTest, MonitorIsNotStarvedByTheSandboxee) {
   std::vector<std::string> envs;
   auto executor = absl::make_unique<Executor>(path, args, envs);
 
-  SAPI_ASSERT_OK_AND_ASSIGN(auto policy,
-                       PolicyBuilder().DangerDefaultAllowAll().TryBuild());
+  SAPI_ASSERT_OK_AND_ASSIGN(
+      auto policy,
+      PolicyBuilder().DisableNamespaces().DangerDefaultAllowAll().TryBuild());
   executor->limits()->set_walltime_limit(absl::Seconds(5));
   Sandbox2 sandbox(std::move(executor), std::move(policy));
   auto start = absl::Now();
diff --git a/sandboxed_api/sandbox2/sanitizer_test.cc b/sandboxed_api/sandbox2/sanitizer_test.cc
index 64f121e..4ba7fd8 100644
--- a/sandboxed_api/sandbox2/sanitizer_test.cc
+++ b/sandboxed_api/sandbox2/sanitizer_test.cc
@@ -130,6 +130,7 @@ TEST(SanitizerTest, TestSandboxedBinary) {
   auto executor = absl::make_unique<Executor>(path, args);
 
   SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder()
+                                        .DisableNamespaces()
                                         // Don't restrict the syscalls at all.
                                         .DangerDefaultAllowAll()
                                         .TryBuild());