diff --git a/core/config.mk b/core/config.mk
index 9e6129017..3664c6c30 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -99,6 +99,11 @@ SRC_TEST_API_DIR := $(TOPDIR)prebuilts/sdk/test-api
 # Some specific paths to tools
 SRC_DROIDDOC_DIR := $(TOPDIR)build/make/tools/droiddoc
 
+# Mark some inputs as readonly
+ifdef TARGET_DEVICE_DIR
+  .KATI_READONLY := TARGET_DEVICE_DIR
+endif
+
 # Set up efficient math functions which are used in make.
 # Here since this file is included by envsetup as well as during build.
 include $(BUILD_SYSTEM)/math.mk
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 12b5869b1..1a367036f 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -241,17 +241,26 @@ SDK_HOST_ARCH := x86
 # or under vendor/*/$(TARGET_DEVICE).  Search in both places, but
 # make sure only one exists.
 # Real boards should always be associated with an OEM vendor.
-board_config_mk := \
-	$(strip $(sort $(wildcard \
-		$(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk \
-		$(shell test -d device && find -L device -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
-		$(shell test -d vendor && find -L vendor -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
-	)))
-ifeq ($(board_config_mk),)
-  $(error No config file found for TARGET_DEVICE $(TARGET_DEVICE))
-endif
-ifneq ($(words $(board_config_mk)),1)
-  $(error Multiple board config files for TARGET_DEVICE $(TARGET_DEVICE): $(board_config_mk))
+ifdef TARGET_DEVICE_DIR
+  ifneq ($(origin TARGET_DEVICE_DIR),command line)
+    $(error TARGET_DEVICE_DIR may not be set manually)
+  endif
+  board_config_mk := $(TARGET_DEVICE_DIR)/BoardConfig.mk
+else
+  board_config_mk := \
+    $(strip $(sort $(wildcard \
+      $(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk \
+      $(shell test -d device && find -L device -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
+      $(shell test -d vendor && find -L vendor -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
+    )))
+  ifeq ($(board_config_mk),)
+    $(error No config file found for TARGET_DEVICE $(TARGET_DEVICE))
+  endif
+  ifneq ($(words $(board_config_mk)),1)
+    $(error Multiple board config files for TARGET_DEVICE $(TARGET_DEVICE): $(board_config_mk))
+  endif
+  TARGET_DEVICE_DIR := $(patsubst %/,%,$(dir $(board_config_mk)))
+  .KATI_READONLY := TARGET_DEVICE_DIR
 endif
 include $(board_config_mk)
 ifeq ($(TARGET_ARCH),)
@@ -261,7 +270,6 @@ ifneq ($(MALLOC_IMPL),)
   $(warning *** Unsupported option MALLOC_IMPL defined by board config: $(board_config_mk).)
   $(error Use `MALLOC_SVELTE := true` to configure jemalloc for low-memory)
 endif
-TARGET_DEVICE_DIR := $(patsubst %/,%,$(dir $(board_config_mk)))
 board_config_mk :=
 
 ###########################################