diff --git a/ChangeLog b/ChangeLog
index 3b6e667d66..2d1f5bcd27 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -54,6 +54,11 @@ Fri Oct 20 20:28:37 2006  Akinori MUSHA  <knu@iDaemons.org>
 
 	* ext/digest/lib/digest/hmac.rb: Follow the framework updates.
 
+Sun Oct 22 05:20:34 2006  URABE Shyouhei  <shyouhei@ice.uec.ac.jp>
+
+        * configure.in: alloca is broken; use C_ALLOCA instead.
+          [ruby-dev:29416]
+
 Fri Oct 20 10:47:43 2006  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* lib/mkmf.rb: fixed the bug of handling COMMON_MACROS.
diff --git a/configure.in b/configure.in
index a9b1874bfb..c1233c65c9 100644
--- a/configure.in
+++ b/configure.in
@@ -515,7 +515,17 @@ fi
 dnl Checks for library functions.
 AC_TYPE_GETGROUPS
 AC_TYPE_SIGNAL
-AC_FUNC_ALLOCA
+case "${target_cpu}-${target_os}" in
+powerpc-darwin*)
+  AC_LIBSOURCES(alloca.c)
+  AC_SUBST([ALLOCA], [\${LIBOBJDIR}alloca.${ac_objext}])
+  AC_DEFINE(C_ALLOCA)
+  AC_DEFINE_UNQUOTED(alloca, alloca)
+  ;;
+*)
+  AC_FUNC_ALLOCA
+  ;;
+esac
 AC_FUNC_MEMCMP
 AC_REPLACE_FUNCS(dup2 memmove strcasecmp strncasecmp strerror strftime\
 		 strchr strstr strtoul crypt flock\