diff --git a/ChangeLog b/ChangeLog
index 9bcd71433b..94f231b673 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+Mon Nov  1 21:25:57 2010  URABE Shyouhei  <shyouhei@ruby-lang.org>
+
+	* main.c: <stdlib.h> is needed, to introduce the getenv(3)
+          prototype declaration.  Without it a C compiler shall infer
+          the getenv type as "int getenv(...);", but this is totally
+          wrong, especially when your machine's sizeof(int) and
+          sizeof(char*) differs.  On such environment a return value
+          of getenv(3), which is in fact a char*, might first casted
+          into a int (loses data here), and then casted back to char*
+          by automatic integral promotion fo fit to the prototype of
+          ruby_set_debug_option().
+
 Sun Oct 31 23:27:09 2010  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (finalizer_table, objspace->final.table):
diff --git a/main.c b/main.c
index a782939ff3..e100cddba5 100644
--- a/main.c
+++ b/main.c
@@ -15,6 +15,9 @@
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #endif
+#ifdef RUBY_DEBUG_ENV
+#include <stdlib.h>
+#endif
 
 RUBY_GLOBAL_SETUP