diff --git a/include/picrin.h b/include/picrin.h
index a1c32c1f..c3373a7e 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -75,15 +75,15 @@ typedef struct {
 
   pic_sym sDEFINE, sLAMBDA, sIF, sBEGIN, sQUOTE, sSETBANG;
   pic_sym sQUASIQUOTE, sUNQUOTE, sUNQUOTE_SPLICING;
-  pic_sym sDEFINE_SYNTAX;
-  pic_sym sDEFINE_LIBRARY, sIMPORT, sEXPORT;
+  pic_sym sDEFINE_SYNTAX, sIMPORT, sEXPORT;
+  pic_sym sDEFINE_LIBRARY, sIN_LIBRARY;
   pic_sym sCONS, sCAR, sCDR, sNILP;
   pic_sym sADD, sSUB, sMUL, sDIV, sMINUS;
   pic_sym sEQ, sLT, sLE, sGT, sGE, sNOT;
 
   pic_sym rDEFINE, rLAMBDA, rIF, rBEGIN, rQUOTE, rSETBANG;
-  pic_sym rDEFINE_SYNTAX;
-  pic_sym rDEFINE_LIBRARY, rIMPORT, rEXPORT;
+  pic_sym rDEFINE_SYNTAX, rIMPORT, rEXPORT;
+  pic_sym rDEFINE_LIBRARY, rIN_LIBRARY;
 
   xhash syms;                   /* name to symbol */
   xhash sym_names;              /* symbol to name */
diff --git a/src/lib.c b/src/lib.c
index b45bb71a..45351083 100644
--- a/src/lib.c
+++ b/src/lib.c
@@ -249,6 +249,18 @@ pic_lib_define_library(pic_state *pic)
   return pic_none_value();
 }
 
+static pic_value
+pic_lib_in_library(pic_state *pic)
+{
+  pic_value spec;
+
+  pic_get_args(pic, "o", &spec);
+
+  pic_in_library(pic, spec);
+
+  return pic_none_value();
+}
+
 void
 pic_init_lib(pic_state *pic)
 {
@@ -257,4 +269,5 @@ pic_init_lib(pic_state *pic)
   pic_defmacro(pic, pic->sIMPORT, pic->rIMPORT, pic_lib_import);
   pic_defmacro(pic, pic->sEXPORT, pic->rEXPORT, pic_lib_export);
   pic_defmacro(pic, pic->sDEFINE_LIBRARY, pic->rDEFINE_LIBRARY, pic_lib_define_library);
+  pic_defmacro(pic, pic->sIN_LIBRARY, pic->rIN_LIBRARY, pic_lib_in_library);
 }
diff --git a/src/macro.c b/src/macro.c
index a95bf66e..e9c9b64b 100644
--- a/src/macro.c
+++ b/src/macro.c
@@ -364,6 +364,7 @@ pic_null_syntactic_environment(pic_state *pic)
   pic_define_syntactic_keyword(pic, senv, pic->sDEFINE_LIBRARY, pic->rDEFINE_LIBRARY);
   pic_define_syntactic_keyword(pic, senv, pic->sIMPORT, pic->rIMPORT);
   pic_define_syntactic_keyword(pic, senv, pic->sEXPORT, pic->rEXPORT);
+  pic_define_syntactic_keyword(pic, senv, pic->sIN_LIBRARY, pic->rIN_LIBRARY);
 
   return senv;
 }
diff --git a/src/state.c b/src/state.c
index 6cd6c139..3402ffb1 100644
--- a/src/state.c
+++ b/src/state.c
@@ -92,9 +92,10 @@ pic_open(int argc, char *argv[], char **envp)
   register_core_symbol(pic, sUNQUOTE, "unquote");
   register_core_symbol(pic, sUNQUOTE_SPLICING, "unquote-splicing");
   register_core_symbol(pic, sDEFINE_SYNTAX, "define-syntax");
-  register_core_symbol(pic, sDEFINE_LIBRARY, "define-library");
   register_core_symbol(pic, sIMPORT, "import");
   register_core_symbol(pic, sEXPORT, "export");
+  register_core_symbol(pic, sDEFINE_LIBRARY, "define-library");
+  register_core_symbol(pic, sIN_LIBRARY, "in-library");
   register_core_symbol(pic, sCONS, "cons");
   register_core_symbol(pic, sCAR, "car");
   register_core_symbol(pic, sCDR, "cdr");
@@ -124,9 +125,10 @@ pic_open(int argc, char *argv[], char **envp)
   register_renamed_symbol(pic, rSETBANG, "set!");
   register_renamed_symbol(pic, rQUOTE, "quote");
   register_renamed_symbol(pic, rDEFINE_SYNTAX, "define-syntax");
-  register_renamed_symbol(pic, rDEFINE_LIBRARY, "define-library");
   register_renamed_symbol(pic, rIMPORT, "import");
   register_renamed_symbol(pic, rEXPORT, "export");
+  register_renamed_symbol(pic, rDEFINE_LIBRARY, "define-library");
+  register_renamed_symbol(pic, rIN_LIBRARY, "in-library");
   pic_gc_arena_restore(pic, ai);
 
   /* root block */