diff --git a/Makefile.rules b/Makefile.rules
index af0c021234a..4702534f267 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -816,6 +816,12 @@ $(LLVM_OBJ_ROOT)/config.status:: $(LLVM_SRC_ROOT)/configure
 	@${ECHO} "****************************************************************"
 	$(VERB) exit 1
 
+# If the Makefile in the source tree has been updated, copy it over into the
+# build tree.
+Makefile :: $(BUILD_SRC_DIR)/Makefile
+	@${ECHO} "===== Makefile out of date, updating from source dir: `dirname $<` ====="
+	cp -f $< $@
+
 #
 # Include dependencies generated from C/C++ source files, but not if we
 # are cleaning (this example taken from the GNU Make Manual).