diff --git a/ChangeLog b/ChangeLog
index 74f5ae79..b1eeb69d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-10-09  Tatsuhiro Tsujikawa  <tujikawa at rednoah dot com>
+
+	Fixed possible underflow.
+	* src/BitfieldMan.cc (BitfieldMan::getNthBitIndex)
+
 2008-10-09  Tatsuhiro Tsujikawa  <tujikawa at rednoah dot com>
 
 	Fixed the bug that last character in URI is not encoded.
diff --git a/src/BitfieldMan.cc b/src/BitfieldMan.cc
index cf3c2333..7940bf25 100644
--- a/src/BitfieldMan.cc
+++ b/src/BitfieldMan.cc
@@ -174,7 +174,7 @@ size_t
 BitfieldMan::getNthBitIndex(const unsigned char bitfield, size_t nth) const
 {
   size_t index = 0;
-  for(size_t bs = 7; bs >= 0; bs--) {
+  for(int bs = 7; bs >= 0; --bs) {
     unsigned char mask = 1 << bs;
     if(bitfield & mask) {
       nth--;