diff --git a/src/trusted/service_runtime/posix/addrspace_teardown.c b/src/trusted/service_runtime/posix/addrspace_teardown.c
index ca1b089c15..08f0483265 100644
--- a/src/trusted/service_runtime/posix/addrspace_teardown.c
+++ b/src/trusted/service_runtime/posix/addrspace_teardown.c
@@ -18,6 +18,10 @@ void NaClAddrSpaceFree(struct NaClApp *nap) {
   uintptr_t addrsp_size = (uintptr_t) 1U << nap->addr_bits;
   size_t full_size = (NACL_ADDRSPACE_LOWER_GUARD_SIZE + addrsp_size +
                       NACL_ADDRSPACE_UPPER_GUARD_SIZE);
+  if (g_prereserved_sandbox_size > 0) {
+    NaClLog(LOG_WARNING, "NaClAddrSpaceFree: can't unmap when memory is prereserved by bootstrap helper\n");
+    return;
+  }
   if (munmap(base, full_size) != 0) {
     NaClLog(LOG_FATAL, "NaClAddrSpaceFree: munmap() failed, errno %d\n",
             errno);
diff --git a/src/trusted/service_runtime/sel_addrspace.h b/src/trusted/service_runtime/sel_addrspace.h
index ad790048a6..1ec2def6a8 100644
--- a/src/trusted/service_runtime/sel_addrspace.h
+++ b/src/trusted/service_runtime/sel_addrspace.h
@@ -94,6 +94,9 @@ NaClErrorCode NaClAllocateSpace(void **mem, size_t addrsp_size) NACL_WUR;
  *
  * Note that this does not free any other data structures associated
  * with the NaClApp.  In particular, it does not free mem_map.
+ *
+ * FIXME: does not work when memory is prereserved by nacl_bootstrap_helper
+ * since we don't know what vm.mmap_min_addr sysctl was
  */
 void NaClAddrSpaceFree(struct NaClApp *nap);
 
diff --git a/src/trusted/validator_arm/build.scons b/src/trusted/validator_arm/build.scons
index 7397eb1646..076acf72e3 100644
--- a/src/trusted/validator_arm/build.scons
+++ b/src/trusted/validator_arm/build.scons
@@ -265,7 +265,7 @@ validator_tests = {
 # The following tests generate ARM nexes from assembly and validate the
 # generate file. They're all expected to fail and produce the golden files'
 # stdout. Stderr is expected to be empty.
-if env.Bit('build_arm'):
+if env.Bit('build_arm') and UsingNaclMode():
   untrusted_env = env.MakeUntrustedNativeEnv()
   for test, exit_status in validator_tests.items():
     nexe = untrusted_env.ComponentProgram(test, 'testdata/' + test + '.S',