diff --git a/core/config.mk b/core/config.mk
index 0920b56..9f8426c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -208,8 +208,10 @@
 # ###############################################################
 # Broken build defaults
 # ###############################################################
-# Assume that all boards have duplicate rules right now.
-BUILD_BROKEN_DUP_RULES := true
+BUILD_BROKEN_ANDROIDMK_EXPORTS :=
+BUILD_BROKEN_DUP_COPY_HEADERS :=
+BUILD_BROKEN_DUP_RULES :=
+BUILD_BROKEN_PHONY_TARGETS :=
 
 # ###############################################################
 # Include sub-configuration files
diff --git a/core/envsetup.mk b/core/envsetup.mk
index a3e78e7..2235219 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -273,6 +273,23 @@
 board_config_mk :=
 
 ###########################################
+# Handle BUILD_BROKEN_* settings
+vars := \
+  BUILD_BROKEN_ANDROIDMK_EXPORTS \
+  BUILD_BROKEN_DUP_COPY_HEADERS \
+  BUILD_BROKEN_DUP_RULES \
+  BUILD_BROKEN_PHONY_TARGETS
+
+$(foreach var,$(vars),$(eval $(var) := $$(strip $$($(var)))))
+
+$(foreach var,$(vars), \
+  $(if $(filter-out true false,$($(var))), \
+    $(error Valid values of $(var) are "true", "false", and "". Not "$($(var))")))
+
+.KATI_READONLY := $(vars)
+
+
+###########################################
 # Now we can substitute with the real value of TARGET_COPY_OUT_VENDOR
 ifeq ($(TARGET_COPY_OUT_VENDOR),$(_vendor_path_placeholder))
 TARGET_COPY_OUT_VENDOR := system/vendor