diff --git a/ChangeLog b/ChangeLog
index e7b893d056..c1cd743671 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 23 23:36:28 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* process.c (proc_setgroups): check if the argument lenght is
+	  modified.  fixed: [ruby-dev:25285]
+
 Thu Dec 23 19:08:41 2004  Tanaka Akira  <akr@m17n.org>
 
 	* rubyio.h: rename FMODE_UNSEEKABLE to FMODE_DUPLEX.
diff --git a/process.c b/process.c
index f3b8426f6d..c42a91903a 100644
--- a/process.c
+++ b/process.c
@@ -2697,7 +2697,7 @@ proc_setgroups(VALUE obj, VALUE ary)
 
     groups = ALLOCA_N(gid_t, ngroups);
 
-    for (i = 0; i < ngroups; i++) {
+    for (i = 0; i < ngroups && i < RARRAY(ary)->len; i++) {
         VALUE g = RARRAY(ary)->ptr[i];
 
 	if (FIXNUM_P(g)) {