diff --git a/apex/Android.bp b/apex/Android.bp
index dce8edd..64836ff 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -146,7 +146,10 @@
         },
     },
     required: [
+        // sign_virt_apex should be runnable from outside the source tree,
+        // therefore, any required tool should be listed in build/make/core/Makefile as well.
         "img2simg",
+        "initrd_bootconfig",
         "lpmake",
         "lpunpack",
         "simg2img",
@@ -167,6 +170,7 @@
         // sign_virt_apex
         "avbtool",
         "img2simg",
+        "initrd_bootconfig",
         "lpmake",
         "lpunpack",
         "sign_virt_apex",