diff --git a/certs/Makefile b/certs/Makefile
index bdddcd21cbb3..d1e0dad038ca 100644
--- a/certs/Makefile
+++ b/certs/Makefile
@@ -22,9 +22,6 @@ $(eval $(call config_filename,SYSTEM_TRUSTED_KEYS))
 # GCC doesn't include .incbin files in -MD generated dependencies (PR#66871)
 $(obj)/system_certificates.o: $(obj)/x509_certificate_list
 
-# Cope with signing_key.x509 existing in $(srctree) not $(objtree)
-AFLAGS_system_certificates.o := -I$(srctree)
-
 targets += x509_certificate_list
 $(obj)/x509_certificate_list: scripts/extract-cert $(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(SYSTEM_TRUSTED_KEYS_FILENAME) FORCE
 	$(call if_changed,extract_certs,$(SYSTEM_TRUSTED_KEYS_SRCPREFIX)$(CONFIG_SYSTEM_TRUSTED_KEYS))