diff --git a/core/base_rules.mk b/core/base_rules.mk
index 7ea9b52..355a22e 100644
--- a/core/base_rules.mk
+++ b/core/base_rules.mk
@@ -20,7 +20,11 @@
 # Users can define base-rules-hook in their buildspec.mk to perform
 # arbitrary operations as each module is included.
 ifdef base-rules-hook
-$(if $(base-rules-hook),)
+  ifndef _has_warned_about_base_rules_hook
+    $(warning base-rules-hook is deprecated, please remove usages of it and/or convert to Soong.)
+    _has_warned_about_base_rules_hook := true
+  endif
+  $(if $(base-rules-hook),)
 endif
 
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