diff --git a/firmware/include/gbb_header.h b/firmware/include/gbb_header.h
index f490bb0..8a21510 100644
--- a/firmware/include/gbb_header.h
+++ b/firmware/include/gbb_header.h
@@ -55,6 +55,10 @@
 #define GBB_FLAG_FORCE_DEV_BOOT_LEGACY    0x00000080
 /* Allow booting using alternate keys for FAFT servo testing */
 #define GBB_FLAG_FAFT_KEY_OVERIDE         0x00000100
+/* Disable EC software sync */
+#define GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC 0x00000200
+/* Default to booting legacy OS when dev screen times out */
+#define GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY  0x00000400
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/firmware/lib/vboot_api_kernel.c b/firmware/lib/vboot_api_kernel.c
index cb9722a..82b9a61 100644
--- a/firmware/lib/vboot_api_kernel.c
+++ b/firmware/lib/vboot_api_kernel.c
@@ -158,7 +158,7 @@
 VbError_t VbBootDeveloper(VbCommonParams* cparams, LoadKernelParams* p) {
   GoogleBinaryBlockHeader* gbb = (GoogleBinaryBlockHeader*)cparams->gbb_data;
   VbSharedDataHeader* shared = (VbSharedDataHeader*)cparams->shared_data_blob;
-  uint32_t allow_usb = 0, allow_legacy = 0;
+  uint32_t allow_usb = 0, allow_legacy = 0, ctrl_d_pressed = 0;
   VbAudioContext* audio = 0;
 
   VBDEBUG(("Entering %s()\n", __func__));
@@ -230,6 +230,7 @@
       case 0x04:
         /* Ctrl+D = dismiss warning; advance to timeout */
         VBDEBUG(("VbBootDeveloper() - user pressed Ctrl+D; skip delay\n"));
+        ctrl_d_pressed = 1;
         goto fallout;
         break;
       case 0x0c:
@@ -286,6 +287,19 @@
   } while( VbAudioLooping(audio) );
 
 fallout:
+
+  /* If defaulting to legacy boot, try that unless Ctrl+D was pressed */
+  if ((gbb->flags & GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY) &&
+      !ctrl_d_pressed) {
+    VBDEBUG(("VbBootDeveloper() - defaulting to legacy\n"));
+    VbExLegacy();
+
+    /* If that fails, beep and fall through to fixed disk */
+    VbExBeep(120, 400);
+    VbExSleepMs(120);
+    VbExBeep(120, 400);
+  }
+
   /* Timeout or Ctrl+D; attempt loading from fixed disk */
   VBDEBUG(("VbBootDeveloper() - trying fixed disk\n"));
   VbAudioClose(audio);
@@ -598,6 +612,7 @@
 VbError_t VbSelectAndLoadKernel(VbCommonParams* cparams,
                                 VbSelectAndLoadKernelParams* kparams) {
   VbSharedDataHeader* shared = (VbSharedDataHeader*)cparams->shared_data_blob;
+  GoogleBinaryBlockHeader *gbb = (GoogleBinaryBlockHeader *)cparams->gbb_data;
   VbError_t retval = VBERROR_SUCCESS;
   LoadKernelParams p;
   uint32_t tpm_status = 0;
@@ -616,7 +631,8 @@
   Memset(kparams->partition_guid, 0, sizeof(kparams->partition_guid));
 
   /* Do EC software sync if necessary */
-  if (shared->flags & VBSD_EC_SOFTWARE_SYNC) {
+  if (shared->flags & VBSD_EC_SOFTWARE_SYNC &&
+      !(gbb->flags & GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC)) {
     retval = VbEcSoftwareSync(cparams);
     if (retval != VBERROR_SUCCESS)
       goto VbSelectAndLoadKernel_exit;
diff --git a/scripts/image_signing/set_gbb_flags.sh b/scripts/image_signing/set_gbb_flags.sh
index ac52432..5469f1a 100755
--- a/scripts/image_signing/set_gbb_flags.sh
+++ b/scripts/image_signing/set_gbb_flags.sh
@@ -31,6 +31,8 @@
   GBB_FLAG_ENTER_TRIGGERS_TONORM      0x00000040
   GBB_FLAG_FORCE_DEV_BOOT_LEGACY      0x00000080
   GBB_FLAG_FAFT_KEY_OVERIDE           0x00000100
+  GBB_FLAG_DISABLE_EC_SOFTWARE_SYNC   0x00000200
+  GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY    0x00000400
 
   To get a developer-friendly device, try 0x11 (short_delay + boot_usb).
   For factory-related tests (always DEV), try 0x39.