diff --git a/ChangeLog b/ChangeLog
index cba6787adf..2f2b527998 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Sun Mar  6 23:26:07 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* process.c (proc_setmaxgroups): added negative value check.
+	  This was suggested by Daniel Berger. Thanks Daniel!
+	  [ruby-core:35426][Bug#4467]
+
 Sun Mar  6 23:18:23 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* process.c (maxgroups, proc_setmaxgroups): increase max groups
diff --git a/process.c b/process.c
index e55c3fda83..a216291595 100644
--- a/process.c
+++ b/process.c
@@ -4713,7 +4713,10 @@ proc_getmaxgroups(VALUE obj)
 static VALUE
 proc_setmaxgroups(VALUE obj, VALUE val)
 {
-    int ngroups = FIX2UINT(val);
+    int ngroups = FIX2INT(val);
+
+    if (ngroups <= 0)
+	rb_raise(rb_eArgError, "maxgroups %d shold be positive", ngroups);
 
     if (ngroups > RB_MAX_GROUPS)
 	ngroups = RB_MAX_GROUPS;