diff --git a/core/config.mk b/core/config.mk
index be2c23b..5ff8ccf 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -275,8 +275,15 @@
 # ---------------------------------------------------------------
 # Generic tools.
 
-LEX:= flex
-YACC:= bison -d
+LEX := flex
+# 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
+# BISON_PKGDATADIR.
+BISON_PKGDATADIR := $(PWD)/external/bison/data
+BISON := prebuilts/misc/$(HOST_PREBUILT_TAG)/bison/bison
+YACC := $(BISON) -d
+
 DOXYGEN:= doxygen
 AAPT := $(HOST_OUT_EXECUTABLES)/aapt$(HOST_EXECUTABLE_SUFFIX)
 AIDL := $(HOST_OUT_EXECUTABLES)/aidl$(HOST_EXECUTABLE_SUFFIX)
@@ -449,4 +456,4 @@
 RS_PREBUILT_LIBPATH := -L prebuilts/ndk/8/platforms/android-9/arch-$(TARGET_ARCH)/usr/lib
 RS_PREBUILT_COMPILER_RT := prebuilts/sdk/renderscript/lib/$(TARGET_ARCH)/libcompiler_rt.a
 
-include $(BUILD_SYSTEM)/dumpvar.mk
\ No newline at end of file
+include $(BUILD_SYSTEM)/dumpvar.mk