diff --git a/ChangeLog b/ChangeLog
index 0a1dc9294d..1fe2bc2e2c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Aug 19 13:18:00 2011  Kenta Murata  <mrkn@mrkn.jp>
+
+	* configure.in: defines _DARWIN_UNLIMITED_SELECT if the target_os
+	  is darwin.
+
 Fri Aug 19 13:14:00 2011  Kenta Murata  <mrkn@mrkn.jp>
 
 	* thread.c: add a description for the behavior of select(2) on
diff --git a/configure.in b/configure.in
index 90586ba633..412ff226d6 100644
--- a/configure.in
+++ b/configure.in
@@ -938,7 +938,7 @@ AS_CASE(["$target_os"],
 [openstep*], [	],
 [rhapsody*], [	],
 [darwin*], [	RUBY_PREPEND_OPTION(LIBS, -lobjc)
-		RUBY_APPEND_OPTIONS(CPPFLAGS, -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE)
+		RUBY_APPEND_OPTIONS(CPPFLAGS, -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT)
 		AC_MSG_CHECKING(whether Mac OS X 10.5 or later)
 		AC_TRY_CPP([#include <AvailabilityMacros.h>
 		    #if MAC_OS_X_VERSION_MAX_ALLOWED <= 1040