diff --git a/include/picrin.h b/include/picrin.h
index b9a2190a..f71fae63 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -52,13 +52,17 @@ typedef struct {
   size_t slen, scapa;
   int uniq_sym_count;
 
-  /* positive for variables, negative for macros (bitwise-not) */
   struct xhash *global_tbl;
   pic_value *globals;
   size_t glen, gcapa;
   struct pic_proc **macros;
   size_t mlen, mcapa;
 
+  /* positive for variables, negative for macros (bitwise-not) */
+  struct xhash *var_tbl;
+  struct pic_syntax **stx;
+  size_t xlen, xcapa;
+
   struct pic_irep **irep;
   size_t ilen, icapa;
   pic_value *pool;
diff --git a/src/gc.c b/src/gc.c
index 23aa1560..fc2f38f2 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -357,6 +357,8 @@ gc_mark_phase(pic_state *pic)
   /* macros */
   for (i = 0; i < pic->mlen; ++i) {
     gc_mark_object(pic, (struct pic_object *)pic->macros[i]);
+  for (i = 0; i < pic->xlen; ++i) {
+    gc_mark_object(pic, (struct pic_object *)pic->stx[i]);
   }
 
   /* pool */
diff --git a/src/state.c b/src/state.c
index a9218430..80367cab 100644
--- a/src/state.c
+++ b/src/state.c
@@ -3,6 +3,7 @@
 #include "picrin.h"
 #include "picrin/gc.h"
 #include "picrin/proc.h"
+#include "picrin/macro.h"
 #include "xhash/xhash.h"
 
 void pic_init_core(pic_state *);
@@ -67,6 +68,12 @@ pic_open(int argc, char *argv[], char **envp)
   pic->mlen = 0;
   pic->mcapa = PIC_MACROS_SIZE;
 
+  /* identifier table */
+  pic->var_tbl = xh_new();
+  pic->stx = (struct pic_syntax **)calloc(PIC_MACROS_SIZE, sizeof(struct pic_syntax *));
+  pic->xlen = 0;
+  pic->xcapa = PIC_MACROS_SIZE;
+
   /* pool */
   pic->pool = (pic_value *)calloc(PIC_POOL_SIZE, sizeof(pic_value));
   pic->plen = 0;