diff --git a/core/config.mk b/core/config.mk
index b928af0..2863e7d 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -587,16 +587,8 @@
 # ---------------------------------------------------------------
 # Generic tools.
 
-LEX := $(prebuilt_build_tools_bin_noasan)/flex
-# The default PKGDATADIR built in the prebuilt bison is a relative path
-# prebuilts/build-tools/common/bison.
-# To run bison from elsewhere you need to set up enviromental variable
-# BISON_PKGDATADIR.
-BISON_PKGDATADIR := $(prebuilt_build_tools)/common/bison
-BISON := $(prebuilt_build_tools_bin_noasan)/bison
-YACC := $(BISON) -d
-BISON_DATA := $(wildcard $(BISON_PKGDATADIR)/* $(BISON_PKGDATADIR)/*/*)
-M4 :=$= $(prebuilt_build_tools_bin_noasan)/m4
+# These dependencies are now handled via dependencies on prebuilt_build_tool
+BISON_DATA :=$=
 
 YASM := prebuilts/misc/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/yasm/yasm
 
diff --git a/core/main.mk b/core/main.mk
index f718c9d..cb8aa60 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -33,6 +33,8 @@
 
 include $(SOONG_MAKEVARS_MK)
 
+YACC :=$= $(BISON) -d
+
 include $(BUILD_SYSTEM)/clang/config.mk
 
 # Write the build number to a file so it can be read back in