diff --git a/core/config.mk b/core/config.mk
index 075af49..b230d0d 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -623,13 +623,13 @@
 # ---------------------------------------------------------------
 # Generic tools.
 
-LEX := prebuilts/misc/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/flex/flex-2.5.39
+LEX := $(prebuilt_build_tools_bin)/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 := $(PWD)/prebuilts/build-tools/common/bison
-BISON := prebuilts/build-tools/$(BUILD_OS)-$(HOST_PREBUILT_ARCH)/bin/bison
+BISON := $(prebuilt_build_tools_bin)/bison
 YACC := $(BISON) -d
 BISON_DATA := $(wildcard $(BISON_PKGDATADIR)/* $(BISON_PKGDATADIR)/*/*)