--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -2450,16 +2450,20 @@ fi
 
 dnl Configure JIT support
 
 case "$target" in
 i?86-*)
     ENABLE_JIT=1
     NANOJIT_ARCH=i386
     ;;
+x86_64*-*)
+    ENABLE_JIT=1
+    NANOJIT_ARCH=X64
+    ;;
 arm*-*)
     ENABLE_JIT=1
     NANOJIT_ARCH=ARM
     ;;
 sparc*-*)
     ENABLE_JIT=1
     NANOJIT_ARCH=Sparc
     ;;
@@ -2473,17 +2477,19 @@ if test "$ENABLE_JIT"; then
 
 AC_DEFINE(FEATURE_NANOJIT)
 AC_DEFINE(JS_TRACER)
 
 case "$target" in
 i?86-*)
     AC_DEFINE(AVMPLUS_IA32)
     ;;
-
+x86_64*-*)
+    AC_DEFINE(AVMPLUS_AMD64)
+    ;;
 arm*-*)
     AC_DEFINE(AVMPLUS_ARM)
     ;;
 sparc-*)
     AC_DEFINE(AVMPLUS_SPARC)
     ;;
 esac