diff --git a/error_code.h b/error_code.h
index aab0917..65a5533 100644
--- a/error_code.h
+++ b/error_code.h
@@ -52,6 +52,7 @@
   kErrorCodeOmahaUpdateDeferredForBackoff = 40,
   kErrorCodePostinstallPowerwashError = 41,
   kErrorCodeUpdateCanceledByChannelChange = 42,
+  kErrorCodePostinstallFirmwareRONotUpdatable = 43,
 
   // Note: When adding new error codes, please remember to add the
   // error into one of the buckets in PayloadState::UpdateFailed method so
diff --git a/payload_state.cc b/payload_state.cc
index f7c75da..6d6791f 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -246,6 +246,7 @@
     case kErrorCodeNewRootfsVerificationError:
     case kErrorCodeNewKernelVerificationError:
     case kErrorCodePostinstallBootedFromFirmwareB:
+    case kErrorCodePostinstallFirmwareRONotUpdatable:
     case kErrorCodeOmahaRequestEmptyResponseError:
     case kErrorCodeOmahaRequestXMLParseError:
     case kErrorCodeOmahaResponseInvalid:
diff --git a/payload_state_unittest.cc b/payload_state_unittest.cc
index eb66628..0eb1875 100644
--- a/payload_state_unittest.cc
+++ b/payload_state_unittest.cc
@@ -86,7 +86,7 @@
 class PayloadStateTest : public ::testing::Test { };
 
 TEST(PayloadStateTest, DidYouAddANewErrorCode) {
-  if (kErrorCodeUmaReportedMax != 43) {
+  if (kErrorCodeUmaReportedMax != 44) {
     LOG(ERROR) << "The following failure is intentional. If you added a new "
                << "ErrorCode enum value, make sure to add it to the "
                << "PayloadState::UpdateFailed method and then update this test "
diff --git a/postinstall_runner_action.cc b/postinstall_runner_action.cc
index 0f8059e..6be13e1 100644
--- a/postinstall_runner_action.cc
+++ b/postinstall_runner_action.cc
@@ -92,6 +92,14 @@
       // to get back to FW A.
       completer.set_code(kErrorCodePostinstallBootedFromFirmwareB);
     }
+
+    if (return_code == 4) {
+      // This special return code means that we tried to update firmware,
+      // but couldn't because we booted from FW B, and we need to reboot
+      // to get back to FW A.
+      completer.set_code(kErrorCodePostinstallFirmwareRONotUpdatable);
+    }
+
     return;
   }
 
diff --git a/postinstall_runner_action_unittest.cc b/postinstall_runner_action_unittest.cc
index 0deb859..128610f 100644
--- a/postinstall_runner_action_unittest.cc
+++ b/postinstall_runner_action_unittest.cc
@@ -92,6 +92,11 @@
   DoTest(true, 3, false);
 }
 
+TEST_F(PostinstallRunnerActionTest, RunAsRootFirmwareROErrScriptTest) {
+  ASSERT_EQ(0, getuid());
+  DoTest(true, 4, false);
+}
+
 const char* PostinstallRunnerActionTest::kImageMountPointTemplate =
     "au_destination-XXXXXX";
 
diff --git a/utils.cc b/utils.cc
index 05e5758..248c665 100644
--- a/utils.cc
+++ b/utils.cc
@@ -966,6 +966,8 @@
       return "TestOmahaUrl";
     case kErrorCodeSpecialFlags:
       return "kErrorCodeSpecialFlags";
+    case kErrorCodePostinstallFirmwareRONotUpdatable:
+      return "kErrorCodePostinstallFirmwareRONotUpdatable";
     // Don't add a default case to let the compiler warn about newly added
     // error codes which should be added here.
   }