diff --git a/core/config.mk b/core/config.mk
index c6e859dcf..abce2b0cc 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -351,7 +351,7 @@ endif
 # ---------------------------------------------------------------
 # Generic tools.
 
-LEX := flex
+LEX := prebuilts/misc/$(BUILD_OS)-$(BUILD_ARCH)/flex/flex-2.5.39$(HOST_EXECUTABLE_SUFFIX)
 # The default PKGDATADIR built in the prebuilt bison is a relative path
 # external/bison/data.
 # To run bison from elsewhere you need to set up enviromental variable
@@ -412,8 +412,6 @@ else
 COLUMN:= column
 endif
 
-OLD_FLEX := prebuilts/misc/$(HOST_PREBUILT_TAG)/flex/flex-2.5.4a$(HOST_EXECUTABLE_SUFFIX)
-
 ifeq ($(HOST_OS),darwin)
 ifeq ($(LEGACY_USE_JAVA6),)
 HOST_JDK_TOOLS_JAR:= $(shell $(BUILD_SYSTEM)/find-jdk-tools-jar.sh)