diff --git a/make_helpers/build_macros.mk b/make_helpers/build_macros.mk
index 9ca6bdf..cb204a8 100644
--- a/make_helpers/build_macros.mk
+++ b/make_helpers/build_macros.mk
@@ -73,6 +73,7 @@
 # Convenience function for verifying option has a boolean value
 # $(eval $(call assert_boolean,FOO)) will assert FOO is 0 or 1
 define assert_boolean
+    $(if $($(1)),,$(error $(1) must not be empty))
     $(if $(filter-out 0 1,$($1)),$(error $1 must be boolean))
 endef