diff --git a/ChangeLog b/ChangeLog
index 771a62fb0d..33381a679e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Apr  3 18:33:38 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* process.c (setreuid, setregid): suppress warnings.
+	  [ruby-core:43374][Bug #6169]
+
 Tue Apr  3 10:18:27 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* enumerator.c (inspect_enumerator): suppress uninitialized
diff --git a/process.c b/process.c
index 3c67bb6396..390cbdb047 100644
--- a/process.c
+++ b/process.c
@@ -113,9 +113,11 @@ static VALUE rb_cProcessTms;
 
 #ifdef BROKEN_SETREUID
 #define setreuid ruby_setreuid
+int setreuid(rb_uid_t ruid, rb_uid_t euid);
 #endif
 #ifdef BROKEN_SETREGID
 #define setregid ruby_setregid
+int setregid(rb_gid_t rgid, rb_gid_t egid);
 #endif
 
 #if defined(HAVE_44BSD_SETUID) || defined(__MacOS_X__)
@@ -4307,11 +4309,11 @@ static rb_uid_t SAVED_USER_ID = -1;
 int
 setreuid(rb_uid_t ruid, rb_uid_t euid)
 {
-    if (ruid != -1 && ruid != getuid()) {
-	if (euid == -1) euid = geteuid();
+    if (ruid != (rb_uid_t)-1 && ruid != getuid()) {
+	if (euid == (rb_uid_t)-1) euid = geteuid();
 	if (setuid(ruid) < 0) return -1;
     }
-    if (euid != -1 && euid != geteuid()) {
+    if (euid != (rb_uid_t)-1 && euid != geteuid()) {
 	if (seteuid(euid) < 0) return -1;
     }
     return 0;
@@ -5010,11 +5012,11 @@ static rb_gid_t SAVED_GROUP_ID = -1;
 int
 setregid(rb_gid_t rgid, rb_gid_t egid)
 {
-    if (rgid != -1 && rgid != getgid()) {
-	if (egid == -1) egid = getegid();
+    if (rgid != (rb_gid_t)-1 && rgid != getgid()) {
+	if (egid == (rb_gid_t)-1) egid = getegid();
 	if (setgid(rgid) < 0) return -1;
     }
-    if (egid != -1 && egid != getegid()) {
+    if (egid != (rb_gid_t)-1 && egid != getegid()) {
 	if (setegid(egid) < 0) return -1;
     }
     return 0;