diff --git a/host/lib/crossystem.c b/host/lib/crossystem.c
index b496259..ba614cc 100644
--- a/host/lib/crossystem.c
+++ b/host/lib/crossystem.c
@@ -62,11 +62,12 @@
 
 /* Masks for kern_nv usage by kernel. */
 #define KERN_NV_FWUPDATE_TRIES_MASK 0x0000000F
+#define KERN_NV_BLOCK_DEVMODE_FLAG  0x00000010
 /* If you want to use the remaining currently-unused bits in kern_nv
  * for something kernel-y, define a new field (the way we did for
  * fwupdate_tries).  Don't just modify kern_nv directly, because that
  * makes it too easy to accidentally corrupt other sub-fields. */
-#define KERN_NV_CURRENTLY_UNUSED    0xFFFFFFF0
+#define KERN_NV_CURRENTLY_UNUSED    0xFFFFFFE0
 
 /* Return true if the FWID starts with the specified string. */
 int FwidStartsWith(const char *start) {
@@ -449,6 +450,12 @@
     value = VbGetNvStorage(VBNV_KERNEL_FIELD);
     if (value != -1)
       value &= KERN_NV_FWUPDATE_TRIES_MASK;
+  } else if (!strcasecmp(name,"block_devmode")) {
+    value = VbGetNvStorage(VBNV_KERNEL_FIELD);
+    if (value != -1) {
+      value &= KERN_NV_BLOCK_DEVMODE_FLAG;
+      value = !!value;
+    }
   } else if (!strcasecmp(name,"loc_idx")) {
     value = VbGetNvStorage(VBNV_LOCALIZATION_INDEX);
   } else if (!strcasecmp(name,"dev_boot_usb")) {
@@ -558,6 +565,14 @@
     kern_nv &= ~KERN_NV_FWUPDATE_TRIES_MASK;
     kern_nv |= (value & KERN_NV_FWUPDATE_TRIES_MASK);
     return VbSetNvStorage(VBNV_KERNEL_FIELD, kern_nv);
+  } else if (!strcasecmp(name,"block_devmode")) {
+    int kern_nv = VbGetNvStorage(VBNV_KERNEL_FIELD);
+    if (kern_nv == -1)
+      return -1;
+    kern_nv &= ~KERN_NV_BLOCK_DEVMODE_FLAG;
+    if (value)
+	kern_nv |= KERN_NV_BLOCK_DEVMODE_FLAG;
+    return VbSetNvStorage(VBNV_KERNEL_FIELD, kern_nv);
   } else if (!strcasecmp(name,"loc_idx")) {
     return VbSetNvStorage(VBNV_LOCALIZATION_INDEX, value);
   } else if (!strcasecmp(name,"dev_boot_usb")) {
diff --git a/utility/crossystem.c b/utility/crossystem.c
index 520f7fd..9a55d17 100644
--- a/utility/crossystem.c
+++ b/utility/crossystem.c
@@ -32,6 +32,7 @@
 /* List of parameters, terminated with a param with NULL name */
 const Param sys_param_list[] = {
   {"arch", IS_STRING, "Platform architecture"},
+  {"block_devmode", CAN_WRITE, "Block all use of developer mode"},
   {"clear_tpm_owner_request", CAN_WRITE, "Clear TPM owner on next boot"},
   {"clear_tpm_owner_done", CAN_WRITE, "Clear TPM owner done"},
   {"cros_debug", 0, "OS should allow debug features"},