diff --git a/make_helpers/build_macros.mk b/make_helpers/build_macros.mk
index 2d2f141..6edc2d6 100644
--- a/make_helpers/build_macros.mk
+++ b/make_helpers/build_macros.mk
@@ -50,6 +50,18 @@
 	$(foreach var,$1,$(eval $(call default_zero,$(var))))
 endef
 
+# Convenience function for setting a variable to 1 if not previously set
+# $(eval $(call default_one,FOO))
+define default_one
+	$(eval $(1) ?= 1)
+endef
+
+# Convenience function for setting a list of variables to 1 if not previously set
+# $(eval $(call default_ones,FOO BAR))
+define default_ones
+	$(foreach var,$1,$(eval $(call default_one,$(var))))
+endef
+
 # Convenience function for adding build definitions
 # $(eval $(call add_define,FOO)) will have:
 # -DFOO if $(FOO) is empty; -DFOO=$(FOO) otherwise