diff --git a/ChangeLog b/ChangeLog
index 20129be290..f7390ec598 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jul 19 03:41:20 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* bignum.c: Added #include <strings.h> for ffs(). Patch by Perry
+	  Smith. Thank you. [Bug #6748]
+
 Thu Jul 19 01:56:02 2012  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* include/ruby/intern.h (rb_num_zerodiv): Added NORETURN.
diff --git a/bignum.c b/bignum.c
index e98648af24..3394825ce8 100644
--- a/bignum.c
+++ b/bignum.c
@@ -14,6 +14,9 @@
 #include "ruby/util.h"
 #include "internal.h"
 
+#ifdef HAVE_STRINGS_H
+#include <strings.h>
+#endif
 #include <math.h>
 #include <float.h>
 #include <ctype.h>