diff --git a/include/picrin/value.h b/include/picrin/value.h
index 42354c78..d14b8a51 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -89,7 +89,9 @@ enum pic_tt {
   PIC_TT_PORT,
   PIC_TT_ERROR,
   PIC_TT_ENV,
-  PIC_TT_CONT
+  PIC_TT_CONT,
+  PIC_TT_SENV,
+  PIC_TT_SYNTAX
 };
 
 #define PIC_OBJECT_HEADER			\
diff --git a/src/codegen.c b/src/codegen.c
index 6aac14b5..57340867 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -658,7 +658,9 @@ codegen(codegen_state *state, pic_value obj, bool tailpos)
   case PIC_TT_UNDEF:
   case PIC_TT_EOF:
   case PIC_TT_PORT:
-  case PIC_TT_ERROR: {
+  case PIC_TT_ERROR:
+  case PIC_TT_SENV:
+  case PIC_TT_SYNTAX: {
     pic_error(pic, "invalid expression given");
   }
   }
diff --git a/src/gc.c b/src/gc.c
index 1c9fddef..23aa1560 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -8,6 +8,8 @@
 #include "picrin/blob.h"
 #include "picrin/cont.h"
 #include "picrin/error.h"
+#include "picrin/macro.h"
+#include "xhash/xhash.h"
 
 #if GC_DEBUG
 # include <stdio.h>
@@ -273,6 +275,24 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
     gc_mark(pic, cont->result);
     break;
   }
+  case PIC_TT_SYNTAX: {
+    break;
+  }
+  case PIC_TT_SENV: {
+    struct pic_senv *senv = (struct pic_senv *)obj;
+
+    if (senv->up) {
+      gc_mark_object(pic, (struct pic_object *)senv->up);
+    }
+    if (senv->stx) {
+      int i;
+
+      for (i = 0; i < 6; ++i) {
+	gc_mark_object(pic, (struct pic_object *)senv->stx[i]);
+      }
+    }
+    break;
+  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
   case PIC_TT_FLOAT:
@@ -397,6 +417,16 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
     PIC_BLK_DECREF(pic, cont->blk);
     break;
   }
+  case PIC_TT_SENV: {
+    struct pic_senv *senv = (struct pic_senv *)obj;
+    xh_destory(senv->tbl);
+    if (senv->stx)
+      pic_free(pic, senv->stx);
+    break;
+  }
+  case PIC_TT_SYNTAX: {
+    break;
+  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
   case PIC_TT_FLOAT:
diff --git a/src/macro.c b/src/macro.c
index 72f4caa1..dca9b8bc 100644
--- a/src/macro.c
+++ b/src/macro.c
@@ -162,6 +162,8 @@ expand(pic_state *pic, pic_value obj, struct syntactic_env *env)
   case PIC_TT_ENV:
   case PIC_TT_CONT:
   case PIC_TT_UNDEF:
+  case PIC_TT_SENV:
+  case PIC_TT_SYNTAX:
     pic_error(pic, "unexpected value type");
     return pic_undef_value();	/* unreachable */
   }
diff --git a/src/port.c b/src/port.c
index 0c3709fd..06a2f5f9 100644
--- a/src/port.c
+++ b/src/port.c
@@ -97,6 +97,12 @@ write(pic_state *pic, pic_value obj)
   case PIC_TT_CONT:
     printf("#<cont %p>", pic_ptr(obj));
     break;
+  case PIC_TT_SENV:
+    printf("#<senv %p>", pic_ptr(obj));
+    break;
+  case PIC_TT_SYNTAX:
+    printf("#<senv %p>", pic_ptr(obj));
+    break;
   }
 }