diff --git a/ChangeLog b/ChangeLog
index 6de2481867..768325e84d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jun 26 00:13:08 2004  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (rb_fopen, rb_fdopen, rb_io_reopen): setvbuf() may return
+	  positive value on failure.  [ruby-dev:23792]
+
 Fri Jun 25 18:07:15 2004  Michal Rokos  <michal@ruby-lang.org>
 
 	* gc.c: bring back _stklen for DJGPP [ruby-core:3084]
diff --git a/io.c b/io.c
index c0cf821b8b..f71ef8f0b6 100644
--- a/io.c
+++ b/io.c
@@ -2381,7 +2381,7 @@ rb_fopen(fname, mode)
 	}
     }
 #ifdef USE_SETVBUF
-    if (setvbuf(file, NULL, _IOFBF, 0) < 0)
+    if (setvbuf(file, NULL, _IOFBF, 0) != 0)
 	rb_warn("setvbuf() can't be honoured for %s", fname);
 #endif
 #ifdef __human68k__
@@ -2424,7 +2424,7 @@ rb_fdopen(fd, mode)
     }
 
 #ifdef USE_SETVBUF
-    if (setvbuf(file, NULL, _IOFBF, 0) < 0)
+    if (setvbuf(file, NULL, _IOFBF, 0) != 0)
 	rb_warn("setvbuf() can't be honoured (fd=%d)", fd);
 #endif
     return file;
@@ -3278,7 +3278,7 @@ rb_io_reopen(argc, argv, file)
 	rb_sys_fail(fptr->path);
     }
 #ifdef USE_SETVBUF
-    if (setvbuf(fptr->f, NULL, _IOFBF, 0) < 0)
+    if (setvbuf(fptr->f, NULL, _IOFBF, 0) != 0)
 	rb_warn("setvbuf() can't be honoured for %s", RSTRING(fname)->ptr);
 #endif