diff --git a/src/parse.y b/src/parse.y
index c8cb37c1..75cc11a1 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -21,10 +21,10 @@ struct parser_control {
 }
 
 %token tLPAREN tRPAREN tDOT
-%token <datum> tSYMBOL
+%token <datum> tSYMBOL tINT
 
 %type <datum> datum simple_datum symbol compound_datum
-%type <datum> list list_tail
+%type <datum> number integer list list_tail
 
 %%
 
@@ -46,6 +46,7 @@ datum
 
 simple_datum
 	: symbol
+	| number
 ;
 
 symbol
@@ -55,6 +56,17 @@ symbol
 	}
 ;
 
+number
+	: integer
+;
+
+integer
+	: tINT
+	{
+	  $$ = $1;
+	}
+;
+
 compound_datum
 	: list
 ;
@@ -96,6 +108,7 @@ pic_parse(pic_state *pic, const char *str)
   struct parser_control p;
 
   p.pic = pic;
+  p.value = pic_int_value(42);
 
   yy_scan_string(str);
   yyparse(&p);
diff --git a/src/scan.l b/src/scan.l
index 27416a63..ddf32b28 100644
--- a/src/scan.l
+++ b/src/scan.l
@@ -1,4 +1,6 @@
 %{
+#include <stdlib.h>
+
 #include "picrin.h"
 #include "y.tab.h"
 
@@ -14,6 +16,7 @@ struct parser_control {
 
 "("	return tLPAREN;
 ")"	return tRPAREN;
+[1-9][0-9]*	{ yylval.datum = pic_int_value(atoi(yytext)); return tINT; }
 [a-z0-9A-Z]+	{ yylval.datum = pic_intern_cstr(p->pic, yytext); return tSYMBOL; }
 
 %%