diff --git a/.github/workflows/build_test.yml b/.github/workflows/build_test.yml
index 22f94477a..2c0254477 100644
--- a/.github/workflows/build_test.yml
+++ b/.github/workflows/build_test.yml
@@ -61,7 +61,7 @@ jobs:
             vm_image: windows-2022
             sdk_platform: windows-amd64
             scons_build_args: platform=x86-64 --no-clang werror=1 mingw_dir=mingw/mingw
-            scons_tests: small_tests medium_tests large_tests disable_tests=run_toolchain_python_tests
+            scons_tests: small_tests medium_tests large_tests
             vpython: pyenv/Scripts/python
             python_packages: pywin32
             mingw_url: https://github.com/niXman/mingw-builds-binaries/releases/download/16.1.0-rt_v14-rev1/x86_64-16.1.0-release-posix-seh-msvcrt-rt_v14-rev1.7z
@@ -79,7 +79,7 @@ jobs:
             vm_image: windows-2022
             sdk_platform: windows-amd64
             scons_build_args: platform=x86-64 --no-clang mingw=1 werror=1 mingw_dir=mingw/mingw
-            scons_tests: small_tests medium_tests large_tests disable_tests=run_toolchain_python_tests
+            scons_tests: small_tests medium_tests large_tests
             vpython: pyenv/Scripts/python
             python_packages: pywin32
             mingw_url: https://github.com/niXman/mingw-builds-binaries/releases/download/16.1.0-rt_v14-rev1/x86_64-16.1.0-release-posix-seh-msvcrt-rt_v14-rev1.7z
diff --git a/SConstruct b/SConstruct
index 69aaa7939..302b25b22 100755
--- a/SConstruct
+++ b/SConstruct
@@ -2131,7 +2131,7 @@ def MakeBaseTrustedEnv(platform=None):
       'tests/unittests/trusted/bits/build.scons',
       'tests/unittests/trusted/platform_qualify/build.scons',
       'tests/unittests/trusted/service_runtime/build.scons',
-      'toolchain_build/build.scons',
+      # 'toolchain_build/build.scons',
   ])
 
   base_env.AddMethod(SDKInstallBin)
diff --git a/src/trusted/service_runtime/nacl_syscall_common.c b/src/trusted/service_runtime/nacl_syscall_common.c
index 926c9352c..227dab02b 100644
--- a/src/trusted/service_runtime/nacl_syscall_common.c
+++ b/src/trusted/service_runtime/nacl_syscall_common.c
@@ -21,6 +21,7 @@
 
 #include "native_client/src/trusted/service_runtime/nacl_syscall_common.h"
 
+#include "native_client/src/include/concurrency_ops.h"
 #include "native_client/src/include/nacl_macros.h"
 #include "native_client/src/include/portability_process.h"
 #include "native_client/src/include/portability_string.h"
@@ -159,8 +160,6 @@ int32_t NaClSysExit(struct NaClAppThread  *natp,
 
 int32_t NaClSysThreadExit(struct NaClAppThread  *natp,
                           uint32_t              stack_flag_addr) {
-  uint32_t  zero = 0;
-
   NaClLog(4, "NaClSysThreadExit(0x%08"NACL_PRIxPTR", "
           "0x%08"NACL_PRIx32"\n",
           (uintptr_t) natp, stack_flag_addr);
@@ -170,10 +169,18 @@ int32_t NaClSysThreadExit(struct NaClAppThread  *natp,
    */
 
   if (0 != stack_flag_addr) {
-    if (!NaClCopyOutToUser(natp->nap, (uintptr_t) stack_flag_addr,
-                           &zero, sizeof zero)) {
-      NaClLog(4, "NaClSysThreadExit: ignoring invalid stack_flag_addr\n");
+    uintptr_t sys_addr = NaClUserToSysAddrRange(natp->nap,
+                                                (uintptr_t) stack_flag_addr,
+                                                4);
+    if (sys_addr == kNaClBadAddress || sys_addr % 4 != 0) {
+      NaClLog(LOG_ERROR, "NaClSysThreadExit: invalid stack_flag_addr\n");
+      return -NACL_ABI_EINVAL;
     }
+    NaClWriteMemoryBarrier();
+    /* Not using CopyOutToUser since this should be atomic */
+    NaClCopyTakeLock(natp->nap);
+    *(uint32_t *) sys_addr = 0;
+    NaClCopyDropLock(natp->nap); 
   }
 
   NaClAppThreadTeardown(natp);
diff --git a/src/trusted/service_runtime/nacl_tls_unittest.c b/src/trusted/service_runtime/nacl_tls_unittest.c
index b5deb5c63..cec5b2843 100644
--- a/src/trusted/service_runtime/nacl_tls_unittest.c
+++ b/src/trusted/service_runtime/nacl_tls_unittest.c
@@ -115,13 +115,15 @@ static thread_return_t OS_API_TYPE ThreadEntryPoint(thread_param_t p) {
   ++g_running_thread_count;
 
   /* Wait for all threads to be running. */
-  WaitForThreads(param->total_num_threads);
-
-  /*
-   * All of the threads have started and have written to their own TLS.
-   * Read our TLS and give it back to the main thread.
-   */
-  param->p_tls_data_return[my_thread_num] = tls_data;
+  if (WaitForThreads(param->total_num_threads)) {
+    /*
+     * All of the threads have started and have written to their own TLS.
+     * Read our TLS and give it back to the main thread.
+     */
+    param->p_tls_data_return[my_thread_num] = tls_data;
+  } else {
+    NaClLog(LOG_ERROR, "WaitForThreads timed out\n");
+  }
 
   return 0;
 }